The trinket pets might be the best option for Priest, but it can also be solod easy as a shaman. Summon pet before he is targeted then put the pet on passive.
you can also use an interupt spell as that is how I targeted all bosses with my shammy.
I had a friend help me on my warlock. They technically dont need to hit him. You just have to be frozen and then broken out of the crystal prison iirc.
I did it on my priest in SL. Basically got naked and used my pet on the dogs. Still kept killing him, but id get 1 piece each time. Best if you can have someone there to help. Honestly it was the hardest part of the quest.
I just tried it with Beth’tilac. I tried so hard not to do any damage and took everything off. I got the fragments, made the focus and brought it to her. She went down and I couldn’t get her to go back up. She wont cast the spell I need on the ground. I tried to run away to reset her and she died. 
All the objectives for Delegation are soloable, but easy to mess up if you missclick and one shot the bosses. Just be super careful.