My Holy priest heals this a lot for guild runs. We've found the following strategy to work pretty well:
- tank Loken where you pull him, don't move him;
- casters stay clear of him throughout, and eat the nature damage aura;
- tank stays with him throughout and eats the Nova;
- melee DPS stay in for Nova, or run out if they want to.
I use Renew / CoH / PW:S on the casters, mostly, and PoM / Renew / CoH on the tank and melee. (I have Improved Renew.) Also you can time a Prayer of Healing to land just after the Nova hits, with a bit of practice.
I find it a lot easier to heal this way, as I'm not running around. To be fair, if we'd just turned 80 we probably wouldn't have the gear to do it