So, I cut a small hole in it, just big enough for Pete to squeeze in through. This "front door" provided the catalyst for rabbitly creativity. The box now looks like this:
Front door, quite expanded.
Side door / window combo. The structural integrity of the box is beginning to get compromised. Pete is NOT worried. Bruno SHOULD be worried. No more perching for the big boy!
(The squeegee is NOT a part of the project...)