I have always heard that Fruit Pectin (sure jell) works. I have heard this since the early 80's when I was just a little nard. I guess it can't hurt but, I recommend at such short notice, either run to the local head shop and get some clean out or additive. If this isn't an option, let the guzzling begin - drink water or tea like mad and in the morning piss a few times before the test only drinking 1 or 2 sugary, vitamin beverages, like energy drinks or gatorade.