In almost all PUGs I've ran in heroic Blood Furnace, we've wiped continuously on the second boss, with little sign of actually beating the encounter. Yesterday me and a friend were testing a few things, and it turns out all the cages are triggered one by one. Going from far right, to far left, to close left, close right, and finally the boss. (I know that sounds a little confusing, so here's the simplified version.)
Without pressing the lever, if your tank walks up to the first cage on the right when ENTERING the room, you can aggro the final 4 pack in the event. After defeating the four, the boss will come out, allowing you to skip 3 waves of mobs, and making the encounter amazingly easier.
I'll post some screen shots later tonight once I rerun it, enjoy!