I park all five shamans on top of each other at max range, and start nuking the instant he is attackable. While standing on top of each other means you eat cleaves, you can just CH out of it, and when the moles appear, you wont get knocked out of los of the boss.
Keep stoneclaw down and a constant stream of magma totems, alongside chain lightning every time its off cd, and he goes down very fast.
I have not actually died yet in any of my kills of him, and have been doing 5 a day, but I think my gear on the Moo's is a pretty big factor.