gistfile1.rb

# my_engine/lib/engine.rb

require "my_engine"
require "rails"

module MyEngine
  class Engine < Rails::Engine
  end
  
  module Routes
    def self.draw(map)
      map.instance_exec do
        match "/my_engine", :to => "my_engine#foo"
      end
    end
  end
end

# my_app/config/routes.rb

MyApp::Application.routes.draw do
  MyEngine::Routes.draw(self)
end

# $ rake routes
my_engine  /my_engine {:controller=>"my_engine", :action=>"foo"}

gistfile2.rb

# my_engine/lib/engine.rb

require "my_engine"
require "rails"

module MyEngine
  class Engine < Rails::Engine
  end
  
  module Routes
    def self.draw(map)
      map.instance_exec do
        match "/my_engine", :to => "my_engine#foo"
      end
    end
  end
end

# my_app/config/routes.rb

MyApp::Application.routes.draw do
  scope "bar" do
    MyEngine::Routes.draw(self)
  end
end

# $ rake routes
bar_my_engine  /bar/my_engine {:controller=>"my_engine", :action=>"foo"}

gistfile3.rb

# my_engine/lib/engine.rb

require "my_engine"
require "rails"

module MyEngine
  class Engine < Rails::Engine
  end
  
  module Routes
    def self.draw(map)
      map.instance_exec do
        scope "baz" do
          match "/my_engine", :to => "my_engine#foo"
        end
      end
    end
  end
end

# my_app/config/routes.rb

MyApp::Application.routes.draw do
  scope "bar" do
    MyEngine::Routes.draw(self)
  end
end

# $ rake routes

bar_baz_my_engine  /bar/baz/my_engine {:controller=>"my_engine", :action=>"foo"}