I wouldn't use Neosporin on the mouth. Also, if you use Neosporin anywhere on a snake, be sure to use the kind that doesn't have painkillers in it. I've known people who say that causes some pretty bad reactions on the scales (even the normal stuff can cause scale problems if you use it too often).
If there's nothing anywhere else on the mouth and no swelling on the inside around the infected area I think you have a decent chance of being able to treat this at home.