How is your healing assigned? We usually have 8 healers with two people specifically designated to heal the raid and the rest on tanks. Also press onto your healers that if someone is in range of them and they can spare a heal to do so, because it's very easy for a clothy to die in just a few seconds. Also if you have the choice use shaman to heal the raid, chain heal is great in these situations.
Another thing that helped us is having a list of people who aren't assigned to click premade and having those who are assigned to click wisper someoen when they die with their group and cube location. This is what managed to save us on this terrible terrible kill:
http://files.filefront.com/MagKillco.../fileinfo.html
Lastly this is a macro I use now so we can check to make sure people are at the right spot for clicking:
/run SetRaidTarget("PlayerName",8)
/run SetRaidTarget("PlayerName",7)
/run SetRaidTarget("PlayerName",6)
/run SetRaidTarget("PlayerName",5)
/run SetRaidTarget("PlayerName",4)
It places icons over the players you want to click the cubes, so now you can look around the room and see if everyone is in the right spot.
For any who watch that video everyone in group 5 was in a clicking group to begin with.