I would try to make the test results look as unreliable as possible. Take caffeine pills or perhaps those drugs you mentioned and go for an indecipherable test. That's what I would do (including the drugs). Or if you're on medication stop taking it if the withdrawal symptoms would mess with the test (if I stopped taking pain meds blood pressure, heart rate and perspiration would be all wacky).
Or maybe drink a ton of water and take the test having to piss really really bad. That'll for sure mess with your ability to be truthful. Or if you can go super Zen that's another way.
But I prefer to lie straight up. If you take the test and fail and someone gives you crap then lie to them. You know those tests are not 100% reliable so you are fine to question them. If they really cared about drugs they'd test you man. Urine is way easy. A polygraph takes more. That's the logic I apply. (Also, I've failed drug tests and told them it was BS and to send it to the lab, which costs money, and they didn't call my bluff and I was fine, so if worst comes to worst there you go.)