Bit of delayed gratification here, but set rules. Subtle ones that won't be noticed by others, like restrictions on speech (don't use this letter, only say this word in the same sentence on that word, etc) and similar ones about food. Make them so that they're essentially impossible and when he inevitably fails, mock him for doing a crap job later on in the night.
Or, alternatively, get him to ask for permission to use the bathroom. Deny it. Watch him squirm. Step it up by taking control of his fluid intake and ordering him to drink more than he normally would.