When I am hand building bottles (and some mugs), I use a dowel with a wooden ball on each end (different diameters) and use it to stretch the belly of the piece by hammering from the inside. What I REALLY need is a similar tool that can be inserted through a narrow mouth/bottle neck then inflated/expanded at one end to perform the same action...then deflate the expanded end so it may be pulled back through the small opening. It would be something like a throwing stick, but one end would be expandable/inflatable.
Make my day and tell me that someone is already making this
P.S. I make all of my tools for creating airways in ocarina construction...lots of unsuccessful experiments to get there, btw.
This sounds very possible. I have an idea of how the base tool could be fashioned around. Would the round end have to be a perfect sphere of would it be advantageous as just a spherical smoothed bodied shape?