I see.
You might want to take a look at Mitch Robinson's sling in the gallery:
http://www.slinging.org/gallery2.html The pics are in the very bottom. He used a gun shape release device and a retention ring to keep the cords together. It is not one strap but the retention ring is suppose to keep the cords from tangling, keep the release cord close to your hand after release, and also keep the stone in the pouch.
good luck with your design and please keep us updated in you finds!