There is a compact M42 bellow that usually came together with the M42 100/4 bellow lens. It weights only about 3 ounce. I have one of those. You can adapter your nikon or Leica M lens easily to a M42 socket.
That thing is nuts! But yeah, making one is definitely on the table. I've fabricated stuff in the past, and bellows are pretty simple devices ultimately so I may go ahead and give it a shot.
