i haven't 5boxed this encounter yet, but i have 2boxed it (with 2 keyboards, not multiboxing). What I did in this situation was just reached over and hit the autorun (numlock) key on the alt after he pulled me in. Given that, I figured what I would do with the multiboxing approach would be immediately follow, and when I get close to the perimeter of the room, hold down the up arrow key (which make ALL my toons move forward, not just the leader) until they hit the wall.