Hello, we do it the following way :
We spread out in all the room, when he targets you, you should not move, juste take his cleave, but everyone else got to be on his back or very far from him. the fact is if you turn while he casts his cleave, he turns with you and cleaves every body in front of him. Only one personne should be hit by the cleave, not more.
(Sorry for my spelling mistakes, i was just cheking the english forums and found that topic, so i tryed to help)