I wrote a thread about it recently and tried it out. Here's my findings:
1) Alcohol helps to move heat from your your core to your skin, which is what you want. It also keeps you feeling warm and inhibits the shivering to some degree.
2) Water removes heat 25 times faster.
3) Fasting helps stop shivering, it's linked to the circadian rhythm and also helps you to drop your body temperature lower when you sleep.
4) You need to be knocked out like totally unconscious.
In my attempt 1: I sat in a very cold bath for about 30 minutes with no alcohol, then laid on the bed for another 30 minutes naked, outside temp c.1C to 2C. After this my body was very cold, i got under the covers and was cold all night, weird body shakes while I warmed up.
Attempt 2: Cold bath for about 45 mins, outside temp about 1C to 2C, then laid naked on bed. Alcohol (not lots - roughly 4 high alcohol lagers) then 1 over the counter sleeping pill chewed up. Out like a light.
I don't know how long i was out for, maybe an hour or 2. Woke up freezing cold and couldn't stand the discomfort so got under covers.
Felt really cold all night, pain in leg muscles and knees, reduced motor function, couldn't stand up, and was seriously cold.
I think the key is to try and cool your core as much as possible first to make the actual time to ctb as fast as possible (alcohol helps with this), then MOST important - take enough additional alcohol and drugs to make sure you're out for several hours.
It's the being out for the count for a long time that will make the difference. If you wake up and you're freezing cold then self preservation will take over.