A synthetic urine system called Quick Fix worked for one of my friends just the other day. It comes with a heating pad and temp sensitive bottle, and it's available in male or female. It says not to let it sit over 12 hrs, but my friend's worked after over 24 hours.

What I suggest is:
have a reliable friend piss in a clean, travel-size scope(mouthwash) bottle
before u go in to piss, heat the bottle up with car heater
use thermometer to stop heating at 98 degrees
stuff against ur crotch in some tight underwear