i would say for sure drink water like mad and exercise a lot. that wont be the only thing but that is sure a start to get out as much as possible. also if they are just doing a home test he can get a detox kit or something like that, that would cover it up or something cause i am sure they would work for that. then just take that about 30 min after his parents spring it on him and say he doesnt have to pee just yet. prob not the best advice but good luck anyways.