Well, I did it. And damn, it was unfulfilling.

Basically leveled up my three characters as soon as I got the airship in that Dinosaur Forest with the Exp. Egg and V/D. After I had them up to about Level 30, did all the sidequests that don't require you getting additional characters (Fanatics' Tower, Ancient Castle, some Narshe stuff, etc.). Made them learn all the magic and leveled up some more and then tackled Kefka's Tower. It wasn't too bad except for instant death attacks on one-member parties... the final fight wasn't as bad as expected either - I made sure to get their magic stats to around 150-200 with the Espers, and had them cast Flare, Meteor, and Merton like crazy. Yay Fire/Ice Shields.

But yeah, it's unfulfilling. No different endings than if you leave out Terra, leave out Locke, or leave out Sabin.