By cancelling Purgatory with either a stun or knockback, he wont get healed from Purgatory. He will however follow you while being untargetable.
Whenever he would normally go out of Purgatory, he will be targetable again, but since he only has 33% hp at this point, any kind of damage will make him cast it again, just make sure to stun him again when he is casting it.
Even though he is untargetable, he can still be damaged by things like Starfall, or Sunfire, if you use it on a target close to him.
By doing this, you avoid getting any hands, and will only have to deal with the slowmoving adds, plus runes.
Gratz on a free skin