How to put app into maintenance mode but still allow admins/moderatos to login and use the site?

I'd like to put my app into maintenance mode but still have admins / moderators be able to log in and use the site.

Two reasons:

1. I'm making some changes within the app that are best applied using the in-app interface rather than the console.

2. Moderators don't have access to the console, but can definitely help with the maintenance tasks we have ahead of us.

How would you recommend this be done? I have been experimenting with setting an environment variable ADMIN_MODE and changing all the permissions when it is true, but that seems pretty cludgy and slow.

I'm using CanCan and Devise, for what it's worth, but I'm definitely open to any suggestions.

This would probably be a fairly simple solution:

class ApplicationController < ActionController::Base
  before_filter :check_admin_mode

  protected

  def check_admin_mode
    if ENV['ADMIN_MODE'] && controller_name != 'sessions' && !current_user.admin?
      redirect_to '/maintenance.html'
    end
  end
end