Why on earth would you want to use Ptex for that instead of epoxy? Ptex does not seal (and is not meant to), does not go into small cracks, does not adhere well, and is much more difficult to work with than epoxy. It adds nothing in this situation.
From the looks of it, I don't see it as that bad of damage. Not enough to clamp w epoxy. Ptex does absolutely go into clear cracks and isn't at all difficult to work with. Dries faster, too. Only thing you would have to worry about is it cracking and falling out. It does seal when it bonds with the base, which you are correct, would not be the case with this situation.
He could also use super glue or duct tape on such a minor little ding if he could figure out how to get it to stay on.