There are no reliable ways to screw with this test. Drinking water will make you 'pass', but the test will show that you drank too much water, and guess how many reasons there are for that? They won't fail you THIS time, but rest assured the next one they give you will be your boss showing up at your desk with the sample jar and escorting you to the bathroom with zero notice.
I'd suggest either finding a job where they don't test you or giving up on the drugs.