The Gibson Co. had a unique idea with one of their resonators on their tenor banjos. It had a trap door in the back that could swing open to also allow sound to escape via the back. The player could then get a little more volume directed toward his ears.

Why folks would have trouble hearing a banjo from any direction is beyond me.

I have not seen these alternate sound ports that you've described by Mr. Beardsell but I did have a particularly vivid and memorable dream some years ago and when I awoke I sketched out what I had seen while I slumbered. It was a similar idea regarding the addition of sound ports in unusual places on the body of a guitar. I've yet to incorporate the idea into one of my guitar projects but still hope to at some future date.