This would be a big undertaking, I know, but perhaps you could consider an auction site of some kind (such as e-Bid), that would let airlines and individuals sell or trade points, awards, certificates, etc. (within the confines of the program restrictions, of course).

WebFlyer would require sellers and bidders to register with a credit card and send items via FedEx (for tracking purposes), and could charge the cards of unscrupulous participants in favor of the wronged party.