You can just have 1 healer stand in the middle area or to the side the two times the tank is on the green head (while everyone else is on purple) so he can reach him. Everyone else stands to the left for the purple head which points towards the middle region. Usually when the tank goes from red/green->purple/green DKs have a bit harder time with the magic from the dot especially with 2+ stacks if they were tanking red and going to green. (At least this is what I've experienced healing it with a DK and Monk tank.) He should only have to do it once as P/G combo is separated by 2 heads.
We had like 3 weeks of banging our heads against the wall wondering why the fight was harder with better gear. Finally one time we brought a (basically) newly 90 mage to the fight and it seemed so much easier.