Fish_Whisperer:The crotch strap will definitely solve this problem for you. I dove my Dive-Rite without a crotch-strap, and it was bad enough that I considered giving it up. With the crotch-strap in place and tightened properly, it will keep your cummerbund and the lower back of the BC where they are supposed to be, and will also keep your tank from riding up and thumping you in the back of the melon. The weights for mine are non-ditchable, although I do have weight pockets in the front, which I use for miscellaneous gear. (and for extra weight if I'm wearing a thicker exposure suit) My weights run along my sides, from just behind my armpits down to the rear sides of the cummerbund. Very comfortable, out of the way, and my trim works out nicely, too.
The only crotch straps I've seen so far are going straight on the "private parts", I don't think I want some strap to be there.
Do you know if there are straps like what they use on a parachute? If I can't find one, I'll probably make one.. I just can't figure out a way to easily disconnect it for emergencies.