Do a search for the "urinator" its like $150 but it comes with 9 volt batteries a microchip, heat sensor, heating pad, and a vinyl piss pouch with a visual thermometer on it all nicely contained in a cloth w/ velcro, it can easily be concealed on the inside of the thigh and you can either load it w/ clean urine from a friend even a woman (who isnt pregnant, props to who knows why, letsee who remembers!) or you can put synthetic urine which can be purchased and mixed up and it comes with one free sample vial of the stuff.
Or you could tie a condom or rubber glove to your leg(no lube, and no talc), but I wouldnt take the chance of it breaking if you like your job, just go get it.
Plus there just isnt enough heat that way, depends how much of a stickler they are on the temp reading out right on your sample.
And for you probation boys theres the whizzinator which includes a prosthetic(sp?) penis.
Good luck.