fake urine is risky but might work, if you can get it in time and if the lab your test is sent to doesn't do extra tests to see if it's real urine like shaking it to see if it bubbles. It's risky I been there. The person giving you the test, if they're really ambitious and trying hard to find someone faking it, may ask if you take daily vitamins because of the color being almost neon, (also the case with flush kits and your own urine) so you say YES I do, everyday! and if asked, remember the name of the vit, like Centrum or Flintstones!
If you try to use your own urine buy a test kit from the local CVS or drug store and take it before you go in, if you fail....
Like they said, If you can find a buddy to piss for you, you could always find something better then a ziplock... A small plastic squirt bottle, something you could buy in a local grocery store, all kinds of stuff uses them. Keep it in the inner thy or overhanging gut if your lucky enough to have one
with ducttape for added security ofc. This is by far your best and cheapest bet and well worth the embarrassment of having to ask someone.