Okay, everyone, let's take it down a notch. You may be familiar with the drug detox kit "Ready Clean". Do you know what is in Ready Clean (and people say that it works)?

B vitamins, minerals, and a little bit of creatine.

So there's something to the B vitamins (niacin being one of them).
Of course you can't make your kidneys more efficient in just one day of taking health foods, but as a general rule, taking care of one's kidneys is important; multivitamins and cranberry juice couldn't hurt.

I won't say you're guaranteed to pass your test, but those are certainly well-founded suggestions.