You need bad gear for this, if you do this with ICC gear, it will just become another AoE slaughterfest - and we're trying to avoid that.
You want a tank with max 26-27k hp with 5man buffs. iLevel 200 stuff max, goes for the whole group.
Do the following:
Story:
Had a bad geared group accidently doing this when my moonkin had just hit 80. This accidental "double" bossfight was rather neat.
It should really be designed like this in the first place, heroic should be heroic.