Depends on how 'serious' an offence he thinks it is- he could coat the dildo in wasabi, or chili oil, or anything of that ilk (hot), and make you keep it inside you for the duration of time you had failed to hold it in the first time. i.e, If he'd said half an hour, you'd still owe 20 min. Or, leave it damp and inside a freezer overnight, then have you hold it in till the ice all melted off. Both of those would seem to me to be 'fitting' to the offence.