You have Lion Heart, so I don't see any major problem. Give Rinoa or Quistis Initiative ability learnt from Pandamona so they'll get first turn, then cast Aura on Squall. If you come into the battle with Squall already on critical (yellow) health, then there will be more chance him using Lion Heart, especially with the Aura.

If you don't like that or you're one of those people who like to beat things the "honourable" way. Cast Meltdown (since you don't have Doomtrain) straight away with the help of Initiative. Cast Triple/Summon Cerberus and give everyone a dose of Protect and Shell. Then Aura around and beat down Bahamut with limits. If your Quistis has Mighty Guard, all the better. If Rinoa has Invincible Moon, sweet. And Renzokuken should own him within a few turns. Have Recover and Revive (learnt from Leviathan and Alexander) ready to go just in case.

Once again, I fail to see the problem with this. I mean, if you can beat Ruby Dragons on Level 100 just to get up to Bahamut, he should be a pushover.