Ok this is a really easy and incredibly cheap way to do it. Took this strategy from someone else's post, here goes.
When first clones spawn use awe and strike each down. Push the emperor away and run down the hall to the stairwell area. Force push him off the edge, if you get the right direction he'll lose massive hp. My first push went from 92% down to 33%. He'll teleport back and summon clones, wait and dispatch them. Depending on his hp he might summon another set of clones, dispatch as well. Repeat force push off the ledge as many times as necessary. Once he dies run back to the throne room and speak to him.
It's a good plan, but not for a Sentinel without Push, or any knockback abilities.