We are using now: Siphon Life, Curse of Agony, Corruption, Unstable Affliction. Then switch to next target. At boss fights those DoTs are followed by 5 (maybe 4 would be better) Shadow Bolts.
Of course the 2nd Siphon Life comes much too early then. But macro length is limited to 255 characters
At least we got dmg contribution up from 15% to 19% so far.

Thats the armory link