The circumstances under which someone would be mentally unstable enough to even try this are irrelevant. If you don't have a bit of ice underneath the snow or at least two non-slushy inches of snow, it probably won't work at all. There are two ways which I found to work:
First figure out, of the right and left breaks, which goes to the front and which to the back. (I don't know if this is standard on every bike; on mine the left is the back and right is the front.)
1.) Start turning in a slow, wide arc. Keep your inside leg slightly off of the pedal so that if you screw up at first you can catch yourself instead of wiping out. At an opportune time, when your outside foot is up, jam it down as hard as you can. This will cause your back wheel to move quickly. If you can keep the front wheel right where it is (turn it sharply while breaking to do this), you'll be rotating-- this is actually kind of like an inverse donut since in a car it's your back wheels that break.
2.) As before, start to turn in an arc, but this time get some speed up. Break only on the side which goes to the back wheel, so that your front wheel will swing around while the back stays put. The faster you're going prior to breaking the better it will be, but you'll also be more likely to fall. This one won't work unless it's sufficiently slippery out.
Don't expect to get this on the first try, and don't think too hard about it. Most of it is intuitively figuring out how you should lean etc. in order to keep your balance but still continue turning.