If anyone has the means to do this, act quickly: funds not spent by Dec 31 (which might be deductible if spent before then) are likely to be taxed as income in the US, to the best of my knowledge.
That said, this seems hard due to correlated risks: if a few clawbacks happen, then probably many do. Amy would need to have a high level of trust that Bill could and would pay out if this happened without going bankrupt himself.
Is it not possible that, if it became public knowledge that grants were insured against clawback, lawyers would try harder to get them? If the money is already spent and it’s a bunch of broke individuals, it may not be worth the expense of trying to claw it back. I guess that would just be something Bill would have to account for.