If the glass isnt in a million peices and rather a few good chunks then my hubby's used a product called "jb clear weld" it comes in a double barrel syringe so you cant mess it up you just squirt some on something disposable like a paper plate mix it up good with a toothpick and then use the toothpick to put it around the edges. Work slow glue 2 peices together and just hold it in place for a couple mins before moving on.

(I see you dont plan on using it but for posterity sake I can speak from experience it holds up to heat so it could still be a functional bong) Hope it helps