I did this on my 4x DKs in heroic several times. At first I wiped a couple times, but like most bosses, once you get the strat down, it's pretty easy from there on out.

Basically, manually position your melee dps behind the boss, when you see dark smash, just hit the back key - so all your melee back up away from the boss. You'll need still need some good heals, but it's not really that bad. Maybe assign healing potions to a key so you can all drink if you get hit.