I know, we tried that a few years ago with a friend of ours who fell asleep after a few drinks. We put his hand in a bowl of luke-warm water. Result? Nothing--we were most disappointed.
It reminds me some years ago I was sleeping and dreamt of a waterfall. It was crystal clear, flowing with the noises and everything. Some people probably would of lost bowel control over this, I however felt thirsty, so I began to drink from the waterfall. I drank and drank, and eventually woke up to find my mouth as dry as a desert and really dehydrated. I guess my body must of reacted like I was drinking but since I wasn't gaining any moisture I wasn't replenishing saliva etc.