I bought a strap system from Gould and Goodrich years ago which allows just any ordinary holster to be strapped on. It is made of a nylon strap to go over the gunside shoulder and provides support and balance with elastic staps across the back to the other shoulder and another down to the belt below. There is a "U" shapped piece of plastic where the holster would normally sit. Simply undo the front strap and place the holster on the the platic "U" with the holster's belt loop and replace the strap. Sounds confusing, but that's just my description, the actual system is fairly simple.
The plastic piece has the id #B 351 stamped on it. I have no idea if Gould and Goodrich still make it or where you could find one.
It works OK, but anything that you fit to is seems a little insecure (Of course, it wasn't designed for it right?) and a thumbreak holster is deffinately required...
