overcap fire/cold/light res 275 - prebuff fade helps with this (similar to preparing for uber trist)
dwarf star + tgods + raven frost = absorb all 3 elements
max block
some phys DR (stormshield and fade is more than enough)
separate the ancients, fight only one at a time
your decoy and valk will help take some attention off you.
the problem is your merc will die, as was said, and then you lose infinity. but i'm not sure if you need the conviction.
all I know is, i've used the above strategy on a SSF HC ES warlock with ~1500 hp, no CTA, successful 3 times and was super easy - nothing could touch me, I even let some phys hits come through deliberately to see. yes I know warlock has a demon tank but i stood in those fire and cold spell abilities that are supposed to hurt, and I let the minions attack me, meh. not a scratch.