I removed the offending plywood wall and traced its shape, then replaced it with a patchwork piece of translucent corrugated plastic (from TAP Plastics).
It makes a HUGE difference in the amount of natural light in the room, and was super cheap and quick.
Total cost: $22.50 for 3 sheets of corrugated plastic. (I provided drill, screws, exacto blade to cut to shape, and clear tape to piece the plastic sheets together.)
Total time: maybe 2 hours to cut, fit and install the lightwall.