Managed to solo this as WHM50 with ample use of Repose, which does not aggro and has no cooldown.

When one of the enemies dies, the rest automatically aggro. However, while sleeping they do not aggro upon waking unless you are in proximity.

As you're about to kill one enemy, you can repose the low enemy you're fighting, re-sleep the rest, and kill the low one. Rinse & repeat~

You can also repose the current target to regen mana.