I took the Cat Nip approach as well. I made Yuna a Gunner and knocked her into critical so that she could do 13 9999s with Trigger Happy. I also made Paine and Rikku jobs with high HP like Dark Knight, Warrior and Berserker (Evade & Counter helps avoid damage) so that they could revive Yuna when she died. If Yuna's luck is high enemies will attack the other two and that would help her last longer. It's a very tough dungeon, but it's beatable with a little luck.