Something someone in a DF run of Ifrit Extreme showed me today. Have the tanks and DPS make a sort of triangle. With both tanks at around 90 or so degrees along whatever edge you're on, so if he attacks one with Incinerate, it doesn't hit the other. and the DPS would make the point of the triangle. This way, except for nails/etc, the tanks can mostly stay in the same spots and just bounce him back and forth.

Like a slice of pie, the tanks are on the outer ring where the cuts are and dps is the point.