Assuming the standard route everywhere is to turn left after the room with the three skeletons, go down those stairs and past the boss room to reach the second switch in the corner, I had a tank go the other way recently and it was so much better.

Turn right as you leave the room, so you don't bump into the tonberry coming up the passage.

Continue around to the right and go down the other set of stairs.

Straight up the corridor to the rusted switch in the corner, then along to the boss room.

I haven't gone back to re-test it, but I think you could avoid ever encountering the big tonberries if you wanted. We dashed past one on the way to the boss room and let it get a few stabs in, since they're not sufficiently lethal to worry about it, but I assume they used to be and I could could never understand quite how you could hope to avoid them without a huge amount of waiting and hiding.