Oh, and: every time you're down there, move the 2x2 area. Make a note for your own personal use.
Hmm. Do burning arrows light wool?
If so, install a hidden dispenser behind a falling lava block to shoot burning arrows onto the jump-off platform. Which is made of wool.
Install a sign that says "Think fast". Just in front of that, put a pressure plate that triggers the dispenser.
EDIT: Apparently not. Maybe a 1x1x1 lava pit near the wool but behind a steel door would do it with the random fireballs?