Solo tanking him and using a Warrior or Paladin OT to taunt most of the adds to them and away from the raid works fairly well, though if the OT gets sucked into Frostmourne the raid will get some pretty impressive burst until he comes out.
If you aren't already, move the Lich King from one side to the other after the Spirits spawn to give the most time for the OT to taunt or to kite them around some to spread them out and lower the burst somewhat.
They fixate on a random person with I want to say 10k initial threat.
"Upon an order we plead, with the lure of a song, a sacred song, to the moon and the stars. An illusionary light is here placed."