Seriously, it's common knowledge at this point, no need to belabor it.
Seeing how I pulled the illidari council about half an hour ago after the 4th tick of my hellfire I'd advise against casting any spell with a mob on target that isn't slapping your raid silly yet. I'd say the initital cast is indeed what proccs it seeing as it hit after the forth pulse and it has some distance to travel. It is a bolt after all.
As for tricks to use it with I doubt there is anything worthwhile. The procc is quite bad and you would have to spamm a spell in order to get a procc. I doubt PVE wise there is anything you can abuse it for.