They should do it the way thy currenty do with a twist.
Reduce all contract amounts for people on PPV by 20 percent. So in total, let's say the old way all the fighters would get 1mm for a card (for a round number). The amounts in the contract are reworked so it is now 800k.
At the end of the card, the fans vote on how to allocate the other 200k. All the votes are averaged and the money is allocated. It would be called a "fan bonus"
If that is too drastic, make it 5 percent. 
they got bigger problems than futbol