gistfile1.txt

class ApplicationController
  before_filter :override_current_user
...

  private

  def override_current_user
    class_eval <<-METHODS, __FILE__, __LINE__ + 1
      def current_user_with_sharding
        do_stuff
        current_user
        do_other_stuff
      end
      alias_method_chain :current_user, :sharding
    METHODS
  end
end