I´ve heard white wine vineger works in masking it due to the high acidity. I don´t know if that is true or not.
A girl who works for me part time and is a huge pot head had to get tested for a job she applied for at the phone co. She drank a pint of the stuff along with about a gallon of water the day of her test and passed.
I think if you piss your brains out before the test it may dilute the ammount in your urine up to the test.