I healed it with a holy paladin (10 man), we took care of one group each - 1 healer, 1 tank and 3 dps in each group. When we let purple go through, I prehotted everyone in my group with Rejuv's before the purple debuff was applied, and kept Lifebloom on myself. I refreshed the Rejuv's and used only Swiftmend and Healing touch and it went just fine. I tried keeping Lifebloom on our lock's felhunter, but he was switching pets and I decided to just put it on myself instead. I guess a hunter pet would be better for this.
As far as I saw, the T12 4 set didn't apply a stack of the debuff (I could be wrong). Our holy paladin claimed that WoG didn't add a stack, but I don't know if that's true. DW mace proc's didn't add a stack.