I suggest to use it on the jeep. Detail it or something. Maybe change the transmission fluid? Seafoam it? I dunno, just sounds much easier than giving it back to just spend it on the jeep. No way he can't accept that!
I'd grab a Visa gist card and then print off a fake "you won" letter with the logo of a local radio station or something and mail it to him or if you know where he banks, just go there and deposit it into his account.