I do it the same way as Khez, apart from the mob I choose to keep alive as well as the pet stance switching. I just prefer passive unless it's necessary to use something else like it seems to be on kael's phase 4. The engineer hits the least and is just generally the best one to leave up in my opinion. His special does nothing as long as you have the staff and its buff.
As you can see from this screenshot, I do not get MCd but I'm able to cast mend pet. Mend pet is also great for grabbing aggro from the phoenix. It's possible to do the same thing on the other side, just make sure kael'thas is closer to the pillar than your pet.