your best option would be to quit for 2 weeks or so, if you do allot of cardio and drink tons of water, especially the day of the test you may pass with flying colors. I went through this 2 summers ago, had a new job, quit for 30 days, then I found out I had to take a hair test....I freaked out, I was shaving my head that summer so after being clean for 45 days or so and head shaving I luckily passed the test.
You can buy THC test kits at the local drugstore.....I have done the quit for 2 weeks routine in the past and that worked.
It also depends, are you lean or do you have allot of bodyfat, leaner people will test clean quicker.
You can also buy a detox kit on the internet( they consist of a viatmin formula and they cost about $150), most piss panel tests can detect those carbo-blocker drinks these days.
I have been a chronic daily smoker for 20+ years, your only real option is to back off for 2 weeks and overload on water.
you could also put clean piss in a condom, tape it to your ball bag and squezze it into the test cup, but most times they watch you piss.
Good luck...
