I love this idea. Maybe I can do this. I am going to darn well try.
Looking at it, you could do it without cutting a hole. Just two pieces of wood the same size and the join it up with a thin bit of ply at the top. The two legs underneath would be used to pin the ply on top with naills, do you think that would work? It would mean I would need to think about using a power tool. I am going to go have a look what I have in the basement.