The sweat test is a small square patch worn on the body for an extended period of time. It's relatively uncommon and usually relegated to test subjects who have a diminished expectation of privacy, such as prisoners, those on probation or parole and military personnel. Manufacturers claim the sweat patch is tamper-proof and no commercial products exist to suborn the device, but one ex-GI did write in to offer HIGH TIMES his ad-hoc solution to the sweat test:

"Right after they put the patch on me, I went home and took a hair dryer and I put it right up to the patch and I held it there for a long time. It got so hot I could barely stand it, but little by little I could pull away just one of the four sides of the patch. Then I took a piece of aluminum foil and slid it in between the patch and my skin and left it there the whole time I wore the damn thing. I puffed like normal, and just before I went to have the patch removed, I pulled out the foil. I put a little adhesive glue on the open edge so it would stick to my skin and passed the patch test with flying colors."

Maybe so, but is sounds like no matter what you do, you're going to get burned.