Step 1: Soulstone as many dps as possible, before phase 3
Step 2: Once you get sucked into the frostmourne room, while everyone is doing their thing to survive, people who were soulstoned run away from rest of the group and blow themselves up by spirit/bombs.
Step 3: Resurrect next to the lich king(raging spirits, vile spirits, and the LK himself won't be active)
Step 4: ????????
Step 5: Profit!
Soulstoning melee is preferred here, as they are completely useless inside frostmourne.
Alternatively you can do this with a brez(die right before frostmourne room part, get brez'd, then accept the resurrection once everyone else are in the frostmourne room), or with shaman's reincarnation.
Warning however, people who were assigned to die needs to die fast in the frostmourne room phase, lichking gets a buff called harvested soul each time someone dies inside the frostmourne room, but if you die early enough the buff will expire before the frostmourne phase is over.