Eh what? Ignore this post if you ever want to get your green fire. This fight has nothing to do with aggro dumping (only on doomguard so pit lord can tank him). And really dump aggro on felhunters? Lol, are you suggesting it's a good idea to get your enslave eaten?
I'm sorry but dumping aggro has nothing to do with this fight. You should focus on lining up your chaos bolt spam with Pit Lords Charge, LoS his Chaos Bolt, kill of the pups while not eating your enslave and keep yourself dispelled at all times.
If you want to know how to execute this fight properly, please take a look at this video:
http://youtu.be/i8jZcA2GUWo?t=9m50s
Be sure to start @ 9 minutes and 50 seconds to see the important part. This video may be a bit lengthy and in depth, but it's definitely one that will help you progress through this fight and teach you what you need to know.