I understand what you mean and of course I will try this!
Cutting out a bigger part of the back panel sounds good – maybe I should buy another Piano 26 to experiment with things like that.
I believe that a workable configuration involving one of more larger holes has promise. The holes in the Cassotto bottom are larger and fewer in number. Using tape again, I have experimented a bit and find that the configuration in this photo works. Even assuming that the Bootay method produces the best results, which I think is probably true, it can be varied and perhaps made easier by working with fewer holes. In my limited efforts with the Bootay technique, I find it easier to employ with fewer holes to work with. Also, the effect of blocking a particular hole is less localized (in terms of relative positions of hole and played key) with the Cassotto because of the larger size of the sound chamber (box).
Some holes here are covered with foam gasket tape and others with blue masking tape. The four splotches of gasket tape in the middle cover the recessed holes. Another configuration: