cancan and authorization on controller actions of a gem.

Hello.
I've installed cancan and bigbluebutton_rails,
https://github.com/mconf/bigbluebutton_rails.
The gem bigbluebutton_rails has some models and controllers, for
example has bigbluebutton/servers_controller.rb.
This controller has some actions like create, join, authorize, etc.
I want that only users with role admin can create.
What can I do?
I need to put load_resource in bigbluebutton/servers_controller.rb?
But it is inside a gem and I think it is not recommended to modify gems code.