I think you could argue that it isn't pay for performance, it's pay for image and the image is valuable if it is present. It's simple enough ... let's say you have an athlete you want to support via NIL.
Offer a base amount, say $200,000.
Eight games, at $100,000 a game. Put in escalators and de-escalators. "For every game, Recipient will dress and take the field if medically cleared to do so. If Recipient does not play, no game NIL funds will be provided. For every game where the Recipient does play, the NIL fee of $100,000 will be paid based on the total minutes played in the game and as outlined in Appendix A. Thirty percent of the total NIL payout will be paid after the end of the season. Failure to play in any post-season game will result in forfeiture of the NIL post-season money."
Something like that.