Sounds like you're describing something like this.



It's a rope release. The ropeloops around the string and hooks back to the release. When the release trips, it releases the rope and lets the string go. Post an item number and I'll take a look and tell you for sure.

You can definitely use a rope release if you hook up directly to the string. I don't know that I'd recommendone for hunting, but they are quite popular for target shooting.