Tanks should have their own variant of "Rescue"

[RajNish]

Actually you can LoS them. Once you head up the slope going up, keep running to the left until you’re about halfway between the corridor walls (but don’t actually go into that corridor) that leads to the second boss. Then you just double back and pull the pack towards the casters who should be just about gathered near the top of the slope and running towards you but stopping at the pillar.

It's enough to wait at the bottom left at the stairs leading to the second boss (stand in the corner all the way), they all come.