Have your buddy piss in a condom. Tie the condom shut, and let it sit in your crotch for a couple hours before the test and keep it there. This way its realistic body temperature. Say that you cant urinate in front of other people and need to be alone. This is a very common condition actually, and perfectly belivable. Have the piss condom in a place you can whip it out like your shlong though just in case. Otherwise go to gnc and get one of those detox pills, but i dunno if thated work.