What I did was wait until he went to the far side of the room, then moved everyone up with them spread out about 10 yards apart. It didn't work the first time as I got a bit too close and aggro'd him with me still bunched up (quick wipe that one). Once I got it down, I had one to the far left, one at the left corner of the path, one to the right corner of the path and one further out right. Hard part is getting everyone spread out enough to avoid the chain lightning without aggroing him until you're ready to pull. :P