I've only experimented thus far, but I found some really nice epoxy in squeeze tubes ,white stuff that looks like pearl when finished. It sticks to horn too, so I made a bi-color horn tip. (Pics tonite). I think it would do well if you can color match it to a horn, and you're worried that the glue lines aren't perfect. Also you don't have to cut into the back of the bow. Just sand it with 120 grit and put it on.
I mix it up (touch more hardener), slap it on with a stick, wait about 5-10 min( a little more sometimes) until it gets a bit hard, and won't stick to fingers. I then mold it into general shape by hand.
Belt sander to shape it down (after 48 hrs).Then it sands by hand nicely.