Perhaps one can make Sauron a nation-specific immobile pretedner with only 1 misc slot, and give this nation (probably ermor) a special transformation spell castable only by Sauron with The Ring.
Say perhaps Sauron is the only one with 8 Death magic (restrict death gem to Mordor only?), and he'll need the ring to give him +2 Death to be able to cast the transformation spell.
Problem is that you have to make sure he can't empower himself or boost his death level via items, which entail item and site editing. Or if possible, edit the cost to empower him in death to 999 gems or greater, which effectively negates the possibility (don't think this is possible right now).
Although that doesn't limit empowering of other mages... And this would only work for human player... I doubt the AI will give the Ring to Sauron if it can get it...
Just some not very useful thoughts...
-Gateway103