I just implemented this last night in my Rails 3.1 project. All you have to do is add the following line to your application.rb:
config.paths['config/routes'].concat Dir[Rails.root.join("config/routes/*.rb")]
Then you can split up your routes however want by adding any arbitrary number of routes files to a new directory config/routes, ensuring that each one conforms to the original signature of:
your_application::Application.routes.draw do
end
This should also work with focused_controller since you are still routing within the normal routes draw block.