This is an awesome thread.
I was having a discussion on the phone with a friend of mine about this (In a more hypothetical tense as to not reveal ideas
) last night, and she and I determined that it would be a legal option assuming that the ball always is in contact with the ground...
The biggest unknown for me was the stitching of the ball and it's effect on creating a seal. Now that it sounds like it is possible, I'll have to do some more digging.