do you feel like the pedals are dropping out from under you when you drop?
if so, try pulling up on the bars and extending your feet down so you're landing more with the rear wheel first. no need to exaggerate this motion, a little is all that's really needed to keep the feet on.
As everyone has said, and I'll say it again, practice is the only way you're going to get the feel of it. Once you do, and unlearn all the bad habits you picked up riding spd's, you'll love platforms.
Do you actually have problems with your feet "bouncing off" or is it just a fear? Cuz I hear people say that occasionally and I have no freakin idea what they are talking about, I ride a hardtail and on the most rooty and rocky trails with my rear tire bouncing all over the damn place I have never had my feet bounce off.
Same here, I've ridden Northstar and D-Ville on a hardtail with platforms, tail end getting beat in every direction and had no problems keeping my feet glued, dont even get slips. It's all techniqe and practice.