You have anyone to cast buffs and another to heal at the same time? I've been fighting them straight on since Fang had about that much HP. Before the battle I equipped everyone with some stuff that helps to reduce the damage from Earth-based attacks, along with the usual stuff for more CP and items.
I use Fang, Sazh, and Hope. Hope heals, Sazh throws on a few buffs, and Fang throws debuffs on the legs. Then I switch so Fang can continue to use debuffs (builds up the gauge faster than other attacks), Sazh uses attack magic, and Hope heals. Switch so Fang can use Highwind, then repeat this for the other leg.
After it falls, use Fang to throw some debuffs on (Imperil, Deshell, and Deprotect mostly), then I switch so Fang can attack and the other two can use attack magic. Keep going until it's at about 950%, then I use Highwind.
Repeat the whole thing about two or three times and it's dead. I use Renew or a Phoenix Down if Hope gets killed off by its Roar attack.