With the raid comp that the OP stated, I'd have the warlock park his pet way back on the stairs and have the rogue pull with tricks to the warlock pet. This prevents a tank from stacking Malevolent Strike to a high number before the pull is even established. The tank who will take Halfus first can release Nether and then grab halfus while the other tank gets storm plus whelps. Pop hero, burn a drake, release time, burn the rest of the drakes while trading halfus back and forth and you're good to go.
Also key is a focus interrupt macro for both tanks and melee. Pop tank cooldowns early and often as well.
The fight really rests on 2 things: establishing the pull properly and interrupting shadow nova every time.