Here's how I do it:

I lean a little forward (you don't have to be waaaay up there). Wait for the right crank to come up to the 10:00 position. While lifting the front (left) pedal (clipped in), I press back on the right pedal which locks the wheel. I keep pressing which actually makes the wheel rotate backwards a bit to around the 8:00 position.

I pump off two of those in emergency situations or when I want to slow down a bit from a moderate pace.

Also, you can do this with any tire. I use Vittoria Diamante Pro racing tires that are *very* sticky. I can lock up while in a sitting position. The key is to pull up with the front pedal, too.