Right. I'm taking the piss out of bitcoin as a whole here, I don't actually think the bitcoin market is mature enough to make shorting on a large scale feasible nor any individual put transaction advisable given the lack of clearinghouses and counterparty risk mentioned by steve8918.

But... the guy has made it clear he believed bitcoin's value would rise, so selling a put option at - say - current value would be advantageous to him. Offer a low enough strike price, high enough premium, and word your offer in layman's terms ("you get money now and might get money later if bitcoin rises or might have to pay money if it falls") and he could be tempted to enter in an appropriate contract.