I did this tonight, and it was fairly annoying; I wiped a couple of times before I got it. I have 1xPally 4xShaman so 'dpsing him down' was not really an option. What I ended up doing was this:

1. Lay down all totems and grounding totem
2. Avenger's shield to pick him up, then turn him to the side immediately
3. As soon as he casts sleep and wipes aggro, hit 'target of target' and use righteous defense.

Righteous Defense is only on a 15 second cooldown, and I never saw him do slumber twice within 15 secs; it appeared to be on a ~20 sec cooldown. He resisted my taunt once (with 12% spell hit; bad luck!) and that was a wipe, but the next time I tried it the taunts all worked and I took him down pretty smoothly with no deaths. Just watch your buffs to make sure grounding totem is still up, and taunt quickly.