MG for single target Soul Swap for multi dotting easy fix. Would have to move some talents around. As long as WIA and SOul Swap are in different tiers it should work nicely. Putting a 20 stacked Agony, Corruption and SL on a new target with 1 global and 1 soul shard would provide us with powerful multi dotting potential without the additional ramp up time at the cost of single target dps as we'd lose MG. ST would still be decent with WIA and SE however so we wouldn't feel completely useless in ST between adds. Maybe just put MG in place of Empowered Life Tap put Contagion in tier 1 in place of MG and put Soul Swap in place of Contagion?
So
Tier 1 would be Haunt WIA Contagion
Tier 2 would be Soul Swap AC MG
You could do Haunt/MG or Contagion/MG or even WIA/MG possibly for pure st spec drain turret spec
You could do WIA Soul Swap for multi dotting with SE for respectable ST