The only one I can think of that might work without altering the story is the Elder from Mysidia. I imagine he would basically function like FuSoYa, but not have all the spells available from the get go. Mainly the super powerful ones like Meteor, Flare, Holy, etc. To make up for this, he has an ability called "Prayer." I don't mean something that heals the party like "Pray." "Prayer" would randomly cast a spell not normally under the Black and White magic sets. It would work a lot like Twin, I suppose, so there would be a someone lengthy charge up time. Plus, that might be a cool way to let the player know that maybe the Twins learned their special "Twin" magic from the Elder's own technique!