In an emergency situation, and you start to backpedal with all the power your legs can muster, you will find yourself in a seated skid. I've done that a few times and it works pretty well. Enough that I started practicing it and it's enough to slow me down to unclip and foot-down-stop if need be.

I have found though, that even a little unweighting of the saddle -- even if you hover above it -- will produce a skid better than a seated one. So try that instead.