That's what a bow sling is for. Any archery shop should carry them.

It goes around the top of your wrist so you can shoot with an open hand and not have to worry about the bow falling out of your grip when the shot goes off.

Gripping the handle generally involves muscles being exerted and some forces are applied on the side of the riser grip. Forces on the side of the grip during the shot are not a good thing to promote accuracy.