diff --git a/GETTING_STARTED.md b/GETTING_STARTED.md
index d24af10..8e92b2b 100644
--- a/GETTING_STARTED.md
+++ b/GETTING_STARTED.md
@@ -149,6 +149,30 @@ Attributes can be based on the values of other attributes using the proxy that i
     FactoryGirl.create(:user, :last_name => 'Doe').email
     # => "joe.doe@example.com"
 
+Transient Attributes
+--------------------
+
+There may be times where your code can be DRYed up by passing in transient attributes to factories.
+
+    factory :user do
+      rockstar(true).ignore
+      upcased { false }.ignore
+
+      name  { "John Doe#{" - Rockstar" if rockstar}" }
+      email { "#{name.downcase}@example.com" }
+
+      after_create do |user, proxy|
+        user.name.upcase! if proxy.upcased
+      end
+    end
+
+FactoryGirl.create(:user, :upcased => true).name
+# => "JOHN DOE - ROCKSTAR"
+
+Static and dynamic attributes can be ignored. Ignored attributes will be ignored within attributes_for and won't be set on the model, even if the attribute exists or you attempt to override it.
+
+Within Factory Girl's dynamic attributes, you can access ignored attributes as you would expect. If you need to access the proxy in a Factory Girl callback, you'll need to declare a second block argument (for the proxy) and access ignored attributes from there.
+
 Associations
 ------------
 
diff --git a/lib/factory_girl/attribute.rb b/lib/factory_girl/attribute.rb
index b217489..8d14256 100644
--- a/lib/factory_girl/attribute.rb
+++ b/lib/factory_girl/attribute.rb
@@ -10,13 +10,18 @@ module FactoryGirl
   class Attribute #:nodoc:
     include Comparable
 
-    attr_reader :name
+    attr_reader :name, :ignored
 
     def initialize(name)
       @name = name.to_sym
+      @ignored = false
       ensure_non_attribute_writer!
     end
 
+    def ignore
+      @ignored = true
+    end
+
     def add_to(proxy)
     end
 
diff --git a/lib/factory_girl/attribute/dynamic.rb b/lib/factory_girl/attribute/dynamic.rb
index 9dc28ff..d421a63 100644
--- a/lib/factory_girl/attribute/dynamic.rb
+++ b/lib/factory_girl/attribute/dynamic.rb
@@ -11,7 +11,7 @@ module FactoryGirl
         if FactoryGirl::Sequence === value
           raise SequenceAbuseError
         end
-        proxy.set(name, value)
+        proxy.set(name, value, @ignored)
       end
     end
   end
diff --git a/lib/factory_girl/attribute/static.rb b/lib/factory_girl/attribute/static.rb
index 85e4df3..becc315 100644
--- a/lib/factory_girl/attribute/static.rb
+++ b/lib/factory_girl/attribute/static.rb
@@ -9,7 +9,7 @@ module FactoryGirl
       end
 
       def add_to(proxy)
-        proxy.set(name, @value)
+        proxy.set(name, @value, @ignored)
       end
 
       def priority
diff --git a/lib/factory_girl/factory.rb b/lib/factory_girl/factory.rb
index 2c8e286..905fd50 100644
--- a/lib/factory_girl/factory.rb
+++ b/lib/factory_girl/factory.rb
@@ -86,7 +86,7 @@ module FactoryGirl
         if factory_overrides.empty?
           attribute.add_to(proxy)
         else
-          factory_overrides.each { |attr, val| proxy.set(attr, val); overrides.delete(attr) }
+          factory_overrides.each { |attr, val| proxy.set(attr, val, attribute.ignored); overrides.delete(attr) }
         end
       end
       overrides.each { |attr, val| proxy.set(attr, val) }
diff --git a/lib/factory_girl/proxy.rb b/lib/factory_girl/proxy.rb
index a9acecd..cb23f28 100644
--- a/lib/factory_girl/proxy.rb
+++ b/lib/factory_girl/proxy.rb
@@ -9,7 +9,7 @@ module FactoryGirl
     def get(attribute)
     end
 
-    def set(attribute, value)
+    def set(attribute, value, ignored = false)
     end
 
     def associate(name, factory, attributes)
@@ -24,7 +24,11 @@ module FactoryGirl
     def run_callbacks(name)
       if @callbacks && @callbacks[name]
         @callbacks[name].each do |block|
-          block.arity.zero? ? block.call : block.call(@instance)
+          case block.arity
+          when 0 then block.call
+          when 2 then block.call(@instance, self)
+          else block.call(@instance)
+          end
         end
       end
     end
diff --git a/lib/factory_girl/proxy/attributes_for.rb b/lib/factory_girl/proxy/attributes_for.rb
index cdac21c..a658f2d 100644
--- a/lib/factory_girl/proxy/attributes_for.rb
+++ b/lib/factory_girl/proxy/attributes_for.rb
@@ -3,14 +3,19 @@ module FactoryGirl
     class AttributesFor < Proxy #:nodoc:
       def initialize(klass)
         @hash = {}
+        @ignored_attributes = {}
       end
 
       def get(attribute)
-        @hash[attribute]
+        @ignored_attributes[attribute] || @hash[attribute]
       end
 
-      def set(attribute, value)
-        @hash[attribute] = value
+      def set(attribute, value, ignored = false)
+        if ignored
+          @ignored_attributes[attribute] = value
+        else
+          @hash[attribute] = value
+        end
       end
 
       def result(to_create)
diff --git a/lib/factory_girl/proxy/build.rb b/lib/factory_girl/proxy/build.rb
index 28cdb09..25aea58 100644
--- a/lib/factory_girl/proxy/build.rb
+++ b/lib/factory_girl/proxy/build.rb
@@ -3,14 +3,23 @@ module FactoryGirl
     class Build < Proxy #:nodoc:
       def initialize(klass)
         @instance = klass.new
+        @ignored_attributes = {}
       end
 
       def get(attribute)
-        @instance.send(attribute)
+        if @ignored_attributes.has_key?(attribute)
+          @ignored_attributes[attribute]
+        else
+          @instance.send(attribute)
+        end
       end
 
-      def set(attribute, value)
-        @instance.send(:"#{attribute}=", value)
+      def set(attribute, value, ignored = false)
+        if ignored
+          @ignored_attributes[attribute] = value
+        else
+          @instance.send(:"#{attribute}=", value)
+        end
       end
 
       def associate(name, factory_name, overrides)
diff --git a/lib/factory_girl/proxy/stub.rb b/lib/factory_girl/proxy/stub.rb
index 3560fcd..73563c9 100644
--- a/lib/factory_girl/proxy/stub.rb
+++ b/lib/factory_girl/proxy/stub.rb
@@ -5,6 +5,7 @@ module FactoryGirl
 
       def initialize(klass)
         @instance = klass.new
+        @ignored_attributes = {}
         @instance.id = next_id
         @instance.instance_eval do
           def persisted?
@@ -42,11 +43,19 @@ module FactoryGirl
       end
 
       def get(attribute)
-        @instance.send(attribute)
+        if @ignored_attributes.has_key?(attribute)
+          @ignored_attributes[attribute]
+        else
+          @instance.send(attribute)
+        end
       end
 
-      def set(attribute, value)
-        @instance.send(:"#{attribute}=", value)
+      def set(attribute, value, ignored = false)
+        if ignored
+          @ignored_attributes[attribute] = value
+        else
+          @instance.send(:"#{attribute}=", value)
+        end
       end
 
       def associate(name, factory_name, overrides)
diff --git a/spec/acceptance/transient_attributes_spec.rb b/spec/acceptance/transient_attributes_spec.rb
new file mode 100644
index 0000000..67ac9f6
--- /dev/null
+++ b/spec/acceptance/transient_attributes_spec.rb
@@ -0,0 +1,68 @@
+require "spec_helper"
+
+describe "transient attributes" do
+  before do
+    define_model("User", :name => :string, :email => :string)
+
+    FactoryGirl.define do
+      sequence(:name) {|n| "John #{n}" }
+
+      factory :user do
+        four  { 2 + 2 }.ignore
+        rockstar(true).ignore
+        upcased(false).ignore
+
+        name  { "#{FactoryGirl.generate(:name)}#{" - Rockstar" if rockstar}" }
+        email { "#{name.downcase}#{four}@example.com" }
+
+        after_create do |user, proxy|
+          user.name.upcase! if proxy.upcased
+        end
+      end
+    end
+  end
+
+  context "returning attributes for a factory" do
+    subject { FactoryGirl.attributes_for(:user, :rockstar => true) }
+    it { should_not have_key(:four) }
+    it { should_not have_key(:rockstar) }
+    it { should_not have_key(:upcased) }
+    it { should     have_key(:name) }
+    it { should     have_key(:email) }
+  end
+
+  context "with a transient variable assigned" do
+    let(:rockstar)           { FactoryGirl.create(:user, :rockstar => true, :four => "1234") }
+    let(:rockstar_with_name) { FactoryGirl.create(:user, :name => "Jane Doe", :rockstar => true) }
+    let(:upcased_rockstar)   { FactoryGirl.create(:user, :rockstar => true, :upcased => true) }
+    let(:groupie)            { FactoryGirl.create(:user, :rockstar => false) }
+
+    it "generates the correct attributes on a rockstar" do
+      rockstar.name.should  == "John 1 - Rockstar"
+      rockstar.email.should == "john 1 - rockstar1234@example.com"
+    end
+
+    it "generates the correct attributes on an upcased rockstar" do
+      upcased_rockstar.name.should  == "JOHN 1 - ROCKSTAR"
+      upcased_rockstar.email.should == "john 1 - rockstar4@example.com"
+    end
+
+    it "generates the correct attributes on a groupie" do
+      groupie.name.should  == "John 1"
+      groupie.email.should == "john 14@example.com"
+    end
+
+    it "generates the correct attributes on a rockstar with a name" do
+      rockstar_with_name.name.should  == "Jane Doe"
+      rockstar_with_name.email.should == "jane doe4@example.com"
+    end
+  end
+
+  context "without transient variables assigned" do
+    let(:rockstar) { FactoryGirl.create(:user) }
+
+    it "uses the default value of the attribute" do
+      rockstar.name.should == "John 1 - Rockstar"
+    end
+  end
+end
diff --git a/spec/factory_girl/attribute/dynamic_spec.rb b/spec/factory_girl/attribute/dynamic_spec.rb
index a209197..2ba78b8 100644
--- a/spec/factory_girl/attribute/dynamic_spec.rb
+++ b/spec/factory_girl/attribute/dynamic_spec.rb
@@ -14,7 +14,7 @@ describe FactoryGirl::Attribute::Dynamic do
 
     it "calls the block to set a value" do
       subject.add_to(proxy)
-      proxy.should have_received(:set).with(name, "value")
+      proxy.should have_received(:set).with(name, "value", false)
     end
   end
 
@@ -23,7 +23,7 @@ describe FactoryGirl::Attribute::Dynamic do
 
     it "yields the proxy to the block" do
       subject.add_to(proxy)
-      proxy.should have_received(:set).with(name, proxy)
+      proxy.should have_received(:set).with(name, proxy, false)
     end
   end
 
@@ -37,7 +37,7 @@ describe FactoryGirl::Attribute::Dynamic do
 
     it "evaluates the attribute from the proxy" do
       subject.add_to(proxy)
-      proxy.should have_received(:set).with(name, result)
+      proxy.should have_received(:set).with(name, result, false)
     end
   end
 
diff --git a/spec/factory_girl/attribute/static_spec.rb b/spec/factory_girl/attribute/static_spec.rb
index ab5300e..cb8f6a1 100644
--- a/spec/factory_girl/attribute/static_spec.rb
+++ b/spec/factory_girl/attribute/static_spec.rb
@@ -12,7 +12,7 @@ describe FactoryGirl::Attribute::Static do
   it "sets its static value on a proxy" do
     proxy.stubs(:set)
     subject.add_to(proxy)
-    proxy.should have_received(:set).with(name, value)
+    proxy.should have_received(:set).with(name, value, false)
   end
 end
 
diff --git a/spec/factory_girl/factory_spec.rb b/spec/factory_girl/factory_spec.rb
index 83eaf7f..01c4711 100644
--- a/spec/factory_girl/factory_spec.rb
+++ b/spec/factory_girl/factory_spec.rb
@@ -309,7 +309,7 @@ end
 
 describe FactoryGirl::Factory, "running a factory" do
   subject             { FactoryGirl::Factory.new(:user) }
-  let(:attribute)     { stub("attribute", :name => :name, :add_to => nil, :aliases_for? => true) }
+  let(:attribute)     { stub("attribute", :name => :name, :ignored => false, :add_to => nil, :aliases_for? => true) }
   let(:proxy)         { stub("proxy", :result => "result", :set => nil) }
 
   before do
diff --git a/spec/factory_girl/proxy_spec.rb b/spec/factory_girl/proxy_spec.rb
index 98fd243..6188780 100644
--- a/spec/factory_girl/proxy_spec.rb
+++ b/spec/factory_girl/proxy_spec.rb
@@ -71,5 +71,14 @@ describe FactoryGirl::Proxy do
       subject.run_callbacks(:after_create)
       object_1_within_callback.should have_received(:foo).once
     end
+
+    it "passes in the instance and the proxy if the block takes two arguments" do
+      subject.instance_variable_set("@instance", object_1_within_callback)
+      proxy_instance = nil
+      subject.add_callback(:after_create, proc {|spy, proxy| spy.foo; proxy_instance = proxy })
+      subject.run_callbacks(:after_create)
+      object_1_within_callback.should have_received(:foo).once
+      proxy_instance.should == subject
+    end
   end
 end
diff --git a/spec/support/shared_examples/proxy.rb b/spec/support/shared_examples/proxy.rb
index cb8a2bc..73325e3 100644
--- a/spec/support/shared_examples/proxy.rb
+++ b/spec/support/shared_examples/proxy.rb
@@ -63,6 +63,14 @@ shared_examples_for "proxy with standard getters and setters" do |attribute, val
     it { instance.should have_received(:"#{attribute}=").with(value) }
   end
 
+  describe "when setting an ignored attribute" do
+    before do
+      subject.set(attribute, value, true)
+    end
+
+    it { instance.should have_received(:"#{attribute}=").with(value).never }
+  end
+
   describe "when getting an attribute" do
     it { subject.get(attribute).should == value }