If they write you a check tell them you will hold the bike until it clears ???
They may only want to pay you back the purchase price, but if you have any big ticket itemsyou did to teh bike I would ask for those as well.
Make sure you get back all you fees to process the bike as well.
Now that's a brilliant approach. Be sure to give them a reason to reject your proposal. If he get's his purchase price returned, he should be grateful.
He is not in a good position to negotiate! They have his money and he has the payments!