cortez:I've never had trouble donning mine (OMS Comfort Harness, SP G250 on 7' Primary, G250 bungeed backup) in the water, although I don't let the primary 7' hose loose - so to speak. I clip of the second stage to the chest D-Ring, but before doing so, wind the hose two or three times - loosely - to make a small circle. It keeps everything tight until you're ready to don. Then I take the backup and basically hold it to the shoulder strap by tucking it under the primary hose. Once the harness is on, untuck the backup and put the necklace on, unclip the primary unwind and wrap normally (FYI - the hangmans special scares me).
I'm at work right now and don't have a picture of how I get my rig ready for in water donning, but I'll snap one tonight and post it for those that are interested.
As promised here are the pictures that I talked about...