Spoon:i have the same idea but it cant seem to materialize. am planning to make a rig that connects my a95 to the two chest d rings.
Here's a pic of my camera rig. There are opposing strap attachment points on the underwater housing. The heavy retractor clips to the right chest D-ring, and the left male clip connects to it's female counterpart on the left chest D-ring. When I'm not taking photos, the harness keeps the camera fairly snug against the chest. When I feel like taking photos, I unclip the left buckle, and release the retractor lock (it's an adjustable type).
If I need my hands real quick for something (like moving a rock), the heavy-duty retractor reels the camera back onto my right chest D-ring. It flops around a bit. If the floppiness becomes a problem, I can always just refasten the the left buckle, and poof! The camera's 2-point secured once more.
My housing has those new Canon modular weights, to offset the housing's inherent buoyancy. Great item to get if you don't have a tray or other attachment to weight your camera down.
Your camera is bigger, and has a larger housing. Your BCD may also have different D-ring locations than my TransPac II. But attachment accessories are cheap, and you could probably get something similar if not identical to work for you.