If I was going to try this I would go for voidwalkers on all the warlocks.

Run with omen - and use the warlocks soul shatter a decent margin before they pull aggro.
I would have manual cast of the voidwalkers taunt on round robin so that if you do pull aggro you can always taunt the elite back (might even work to move the elite on to a full health voidy so the first one can be healed up).

I'd probably try this as affliction and let the dots eat away so there would be less burst aggro gain.
I'd make sure I had points in demonology for the demonic brutatily talent for improved taunt.