I'd say do all three.
Have him make a revenant wizard, artificer, or other arcane class. Have him take the Death's Blessing feat, which in addition to other perks means he is no longer considered a living creature. Then have him get and use the Lich Transformation ritual at level 14. Then have him take the Archlich epic destiny.
That's about as lich-like as you can possibly get as a PC, I think.
Edit: Oh wait. I missed the point of the first post -- this is an existing level 14 character. Well, Lich Transformation plus Archlich epic destiny should be pretty good, I think! But if you don't like the lich template or it doesn't fit, tweak it to suit, maybe drawing from revenant race features and feats for inspiration.