Anyone remembers the bug where dismissing the eye of kilrogg will get you aggro on whatever your target is? Well, that exploit is something similiar (but sadly a bit more complex to do)
As Affliction, you have a talent called "Pandemic" that is refreshing your dots when you cast Drain Soul on a target below 25%. The interesting part is, it tries to refresh the dots on your current target instead of the mob you cast Drain Soul on.
And that leads to aggro on your current target.
So, what you have to do to pull anything you can target
1. Get a mob below 25%
2. Cast Drain Soul on him
3. Target whatever you want to pull and wait till Drain Soul ticks
Great example: Sjonnir the Ironshaper in Halls of Stone.
Cast Drain Soul on the first trash when they are below 25%, use a target macro "/tar sjon", wait for him to run through all the walls right next to you
Edit: Obviously you don't need a target below 25% anymore. It works regardles of the percent, even with critters. Which makes that exploit way easier