Gentlemen, please calm down.
Brooks said:
I actually don't see how he or Ewan can return unless maybe it's as ghosts, in which case there would a lot of force ghosts running around (we already have 3)
It's easy! You just have them show up in some hologram (or holocron, even) that Luke finds in the Jedi Temple or somesuch that teaches him about Jedi history or whatnot.