I did it as a disc priest
heres a video:
https://www.youtube.com/watch?v=dfa31bPDpwQ
I used HWF class trinket and used spirit shell to negate the fire damage during progression. Not necessary, but it did make it easier to heal. Make sure you know right away that clarity of will is not worth using. Its slow cast time means someone else has to be healing you quite a bit as well. Using flash heal (or SS+flash heal) as your spam means that people only need to help you if you have ~15 stacks of fire or you let yourself get too low (something I had happen when I spent too much time healing other players with fire)