All you do is open a new section of the forums, and server owners have to put in a request to get a license, the licesnse can be revoke at anytime. And only licensed server owners can get the server files.
That's how I would liek it to be done anyways. It is how PR does it which works great.
And if they try to run the server without a license, all players see is a black screen, right?
"One of the bitches actually gave birth while she was attacking, and her puppies joined in on the carnage."
--the awesomeness that is Boatmurdered.