I don't even remember how I beat Emerald, but I was tired and didn't want to actually spend time fighting Ruby so I set up these materia:

Last Stand - Phoenix, Last Stand - KotR, Last Stand - KotR, Last Stand - Leviathan
Last Stand - Bahamut, Last Stand - Bahamut, HP↔MP - EXP Plus

I think I did that for everyone with different summons. That way as soon as the battle started I just continuously hit the attack button and every time he hit someone he would take a crapload of damage but the party would be okay. At least I think. It's been a while.