Would it be possible...

You can always change an actor (like one of the moogle) and make a temporary character that would replace another one if he hasn't been recruited yet.

At the start of the game, all PC"s are turned into moogles. THis is possible since everyone except for terra and locke are permanent characters. Once a character has joined the party, not even event hacking allows you to replace that PC by a moogle or something.