Substitution simply isn't a viable option, maintaining the proper temperature would be too difficult. Also they stand outside a thin door and listen to you, fumbling with a ziploc or some other apparatus would be noisy.

Also, apparently if the sample comes back diluted they just make you wait about an hour before you give another sample.

I know a few guys that have passed on forty eight hours notice with these detox drinks. I'm confident that i'll pass as long as I get the necessary time frame in before the test.