+1 for sticky Epoxy.... I wouldn't do it. There is a reason everyone uses it as a grain filler and follows up with Poly or Lacquer. For the most part unless Epoxy is fresh it might not harden clear and hard. I have had the worst luck with local Epoxy that was on the shelf too long.
I have had good success with ZPoxy from the local Hobby store, it dries fast, hard, buffs well and was able to use it to repair the finish on my Road Flare Red RG550. However I would not finish a guitar in it.