I run with plate-wearing tanks, so it may not be totally relevant ... but I was only able to beat the dragon boss by hitting the AH and buying fire resistance gear. I had a lot of trouble with him on two different teams 'til I dumped a bunch of +fire resist on the tank and then had no trouble at all. This is theory, but it seems to me that if you stack one shaman with as much fire resistance as you can and sort of tank with him, the shamans' natural inclination to annihilate things in short order will solve the rest.