If you use a software solution like Innerspace, Hotkeynet or Keyclone, they can mouse broadcast.
I personally use keyclone.
If each wow window is as the same aspect ratio, and the hotkey to turn mouse broadcast is set to on, anything clicked (right or left) on one screen will be clicked at about the same point on the others. So I can press Shift-H, which is my PvE Hurricane macro on all druids, and then F7 which is my toggle mouse broadcast on/off, and left click where I want it. The other druids will put it in approximately the same point. When done AoEing, another F7 turns mouse broadcast off.