This can be done with a Warlock and a Death Knight. They don't have to both be in group, it just works with either class.
As you know when you step into a Feed Pool Feed Pool - Spell - World of Warcraft you get a stacking debuff that does stacking damage the more pools you absorb. Immunities and the like do not work to absorb the pools and you just have to stand in it to make it go away.
I found that after you are done absorbing pools you can:
As a Death Knight: Just before the debuff for the stacking damage is about to wear off, about four seconds left, you can use Anti Magic Shell. When the debuff is to wear off the Secondary stacking permanent debuff which increases the damage you take from the pools will not apply.
As a Warlock: If you are talented into Soul Leech during this fight, you want to make sure that you have the shield buff just before the stacking debuff is about to wear off. Once it does wear off, the secondary stacking permanent debuff will not apply to you.
I am unsure if this works with a Priest's Power Word: Shield or a Paladin's short bubble cd.
I have kept the path between my demon gate clear the entire fight with no secondary debuff applying. Hope this helps some of you stuck on this fight.