Esto tambien lo soluciona.....

controller_helpers.rb

module AbTests::ControllerHelpers

  def randomize_ab_version
    "rtc"
  end

  def get_ab_version
    if params[:ab_version]
      cookies[:ab_version] = params[:ab_version]
    else
      # cookies[:ab_version] ||= randomize_ab_version
    end
  end

  def redirect_to_ab_version!
    if get_ab_version == "rtc" and not request.host.include?(get_ab_version)
      redirect_to "http://#{get_ab_version}.#{request.host.gsub("www.","")+request.fullpath}"
    end
  end

end