Rails: Workaround to place variant in URL

gistfile1.rb

class ApplicationController < ActionController::Base
  before_filter :set_variant

  def set_variant
    if request.format == :mobile
      if request.xhr?
        request.format = :js
      else
        request.format = :html
      end

      request.variant = :mobile
    end
  end

  def url_options
    defaults = {}
    defaults[:format] = request.path_parameters[:format] if request.variant.try(:include?, :mobile)

    super.merge(defaults)
  end
end