If you really gotta stop in the shortest distance, using both brakes will stop shorter. Admittedly most of the braking force is coming from the front, but you're getting some from the back, particularly if you really weight the rear wheel. More rubber generating more friction against the road = faster stopping.
Only downside is you can skid the rear tire, but 1) that's easy to modulate, less pressure when it starts to lock, and 2) a rear skid is rarely a big deal.
I try to avoid using the rear brake much, particularly in groups, but if I'm about to get plowed by a car, I'm using all the brakes available to me.