if you have wakka's attack reels then this'll be a breeze. i don't think you can get it at thaty point if u haven't already cos ur not allowed to blitz.

charge everyone's ODs before the fight

have your 3 fastest characters in battle first to get the moves in first. have tidus cast slow on him till it takes effect. have everyone use their most damaging Ods then switch in ur 3 most powerful melee attackers, have tidus cast hastega then just go nuts with normal attacks. if you need to bring rikku in for al bhed potions make sure she is hasted too.

if evrae draws breath only move out if cid has a go before evrae, if not jus keep pummelling.