The only thing I think that might work then is building it back out with a colormatched epoxy of some kind.Turns out the pipe is a pre-transition Barling, so if I can salvage the original stem that would be the goal. However, if all else fails this will be the route I go.
Come to think of it I have deer antler already at my house and that would probably work well. If not, Vermont Freehand carries ox horn slices.If you can get another piece of horn you can grind a bit into powder then mix that with some CA and make a putty. Fill with the putty, let it dry/cure fully, then sand it smooth.