Agree - have some fun. Tell him you'll ship next week. Then when he calls - say you forgot. Promise him you ship right after Christmas. Then when he calls back promise you'll ship next day, and so on.
Or, try this - tell him you've contacted the Monrovia CA police and the US Post Office and they'll be contacting him in person tomorrow - just to clear this whole thing up.
BTW, the bank may not be interested, and the police may not be interested - but I'd bet the Post Office would be interested. Isn't using the mail for a scam a Federal Crime - called Mail Fraud?