I'm not a big fan of soft sided ball, or shot, bags. But, I have made several in the past. The most successful ones were made with an antler nozzle. They were secured with a fine piece of stranded copper ground wire from the hardware store. I filed a groove in the antler nozzle, slipped the neck of the bag up over the nozzle far enough so it can be pulled back down over the wire, creating a collar, then the wire is twisted up tight, and soldered with soft solder, after dampening the leather with a little water.
Oh, and by the way, I wouldn't pull the stopper of my ball, or shot, bag out with my teeth for love, or money.
Hungry Horse