Cardio. Anything to increase your metabolism. Drinking water doesn't hurt either. Lots of people will say it doesn't help unless you do it the day of the test, but drinking water DOES increase your metabolism, which means it'll get out of your system faster.

You should be clean already though. I pissed clean after 18 days of abstaining.

In fact I think I might have pissed clean after smoking the night before a test and simply drinking lots of water (but only pissing once or twice before the test, 3 hours before it)