Consciously lean toward the unclipped foot, so that foot has to step down to hold you up. One way to make sure you do this is to steer toward the clipped foot side. So if you unclip your right foot, as you come to a stop, steer a bit to your left and lean toward your right. Boom- you'll fall over if you don't put your right foot down, just the way you want it.

Practice this several times until it becomes second nature. Once you master it one side, do it for the other until your brain just makes all the right adjustments for the foot you're unclipping.