Without being able to know a date..it would be hard to do. Before I've been aware of the date of my test...I smoked every day, lol. But the day of the test I just drank a shitload of water all day and pissed out only clear water all day..passed the test fine. That's the only advice I can give you aside from not smoking at all until you get a different job?

edit: any amount is going to be detectable...that's the target of drug tests...is marijuana.