As a Jedi master, if you have the characters in your party when you do something that earns light side points, they will jump significantly toward the light side. This even applies to the evil NPCs. It's quite easy to get lightside characters to lightside mastery this way. Unfortunately, loading a save game resets the alignment of whichever 2 are your current companions and loses the mastery, with the exception (for some reason) of Visas.