If your fingers are fast enough, you can use Irvine's Quick Shot and Zell's limit break. One time I had 30 seconds on Zell's limit, and it took me a total of .25 seconds to do Booya and Punch Rush. With each hit, I knocked off around 3k-3.5k hp (if Zell is maxed out with a lot of strength, you can hopefully do max damage), so if you multiply that by the number of possible hits, in my case was around 110-120 combos. So when he's done with that, he knocked off a whopping 360k damage. That's if you are fast enough, and have an amazing timer. Make sure you have spd junction with maxed out triples. That way you can make your characters pretty fast. Cast aura on all three. If Rhinoa is good enough, use Invincible Moon, a wonderful limit break, and then go again with Zell's limit break, and with Rhinoa's Invincible Moon and Wishing Star limit breaks. On the side have Irvine use quick shot, although you are limited to only 100 of each ammo, you can still do somewhat decent. My advice is stock up on magic and get some junction scrolls if you dont have them for each GF. If Zell is fast enough, and if you are lucky enough, you would do over with Omega in half an hour. Just hope that your characters are fast enough to cast triple and aura on all. Cast full life when someone dies, if two dies, hope that triple is still in there and cast full life on the other two, repeat process until Omega is dead.

(I was lucky enough where Rhinoa kept using Invincible Moon when I needed it, and for the most part when I didn't, Wishing Star and sometimes Angelo Cannon)