When I had that problem (for instance when borrowing the bike of my 6'4" "baby" brother), what I do is a sort of jump forward off the seat as I'm stopping. Basically, hit the breaks and stand up on the pedal that is at the bottom of the stroke lifting my butt of the seat and then just as the bike stops, put the free leg on the ground or jump off and put both feet on the ground. Just takes a little practice to get the timing right of jumping off just at the point when the bike has stopped, not two seconds before when the seat will hit you in the back. It is possible to get used to it, just takes a little practice.

Good luck!