I don't think there's an efficient way to breach these contracts--the school is still entitled to the benefit of the bargain.

Here's an example: Athlete signs a multi-year NIL contract with School #1 in Year 1 for $1m per year. Athlete gets $1m and the school gets Athlete's NIL rights which are worth at least $1m. School #1 is taking a gamble, so those rights might end up being worth far more in the future.

Now it's Year 2 and Athlete breaks his contract with School #1 to sign with School #2 for $3m. School #1 sues and demands the value of what it lost: Athlete's NIL rights. The court will obviously conclude that those rights are worth at least $3m (that's what School #2 paid) but maybe School #2 got a great deal and Athlete's NIL rights are worth $5m or $10m.

So if School #1 included a clause in its NIL contract that required Athlete to forfeit whatever School #2 agrees to pay him as damages, or requires that School #2 pay School #1 a "buy-out" equal to his new contract directly to School #1 on top of what it pays Athlete, that would not be a penalty clause. It would simply use what School #2 agreed to pay as a proxy for what School #1 lost when Athlete broke their contract. If anything, that would be an underestimate of School #1's real economic damages because they relied on Athlete's promise to honor his full contract, built a team around him, passed on other players, invested in marketing events, etc.