I use a focus;alt modifier with the following spells: Shadow bolt, Corruption, UA, and BoA.
I start my rotation on the main dps target as usual: SB>Haunt>DS>BoD>Corr>UA
I then use my focus;alt modifier and cast: UA>Corr>BoA>Shadow bolt (making sure I get all my dots applied while under DS)
After that, I do all I can to keep both targets at max x3 shadow debuff by casting all Shadow bolts on the focus target and casting Haunt on my main dps target immediately (or as close as possible) when it's ready to make sure the stacks stay in place. I also cast a Nightfall proc on the main target every so often as not to loose the shadow and flame debuff.
It's not always perfect, especially on Shannox since a dog sometimes gets in a trap and you loose your stacks, but it's a terrific challenge to keep the targets as dotted and debuffed to the maximum potential.
Our last WoL
I didn't play perfectly (forgot DG of all things) but that's always the challenge!
To keep track of the dots, I use Powerauras for my main target, and keep my peripheral vision on dotimers for the focus target. I don't even bother with SSwap, all it does is give the illusion of efficiency. Given the actual GCD's used, slight big of lag in re-transplanting, and long cooldown, it saves 0 time.