well what i did for my tests was, i got my friend who doesnt smoke to piss in a small plastic bottle and stored it outside of my window burried in a foot of snow.(luckily it was winter) whenever a test came up i got the bottle, heated it by sitting it in hot water in the sink, and used a fish tank thermometer to make sure it was around 96-98 degrees. after each test i'd get my friend to get me a refill. since you probly have no snow outside right now, you can try hiding it way in the back of the freezer.
if you dont go with that, my only other advice is to try dillution
(bassically when they tell you you need to take a test, insist that you simply have no pee in you and to wait a half an hour. then find a way to drink a good 2-3 litres of water.) hopefully that will dillute the thc out of your pee. also, ive heard that the highest concentration of thc can be fround in the beginning and end of your stream, so dont let the first or last drops into the testing cup.
my explanation of dillution was a quick one though, defintily check out the drug testing section and read up more on dilluition, and remember that it is possible to OD on water so dont overdo it lol.