Al,
Bill M. (Misiaszek?) that posts on: http://groups.yahoo.com/group/hhpa/ and on message, #13238, Bill M. has a Vimeo posting http://vimeo.com/26454691
On that video go to 0:25 and then again at 2:05 and watch him release with his right hand from Aero tow. He releases by bending his wrist down.
Perhaps a release like Bill M. uses for Aero towing and rigged to a Tad E. straight, pin, barrel release would work off of boat platform towing.
This might even work for payout running behind the truck launching. It would not have the climb restricting bridle rope to the keel and a driver could get your nose too high near the ground. I don’t like that idea but at least you could release without letting go.
An in the teeth release like Tad posts about would be another way of doing either style of towing without the need to take your hands off the control frame.
Platform towing will take away the running part of launching and have you safely above stall speed before you release from the platform. This would take you out of the situation you were in running and not being able to let go to release.