You could make an internal male mold out of balsa or cheap pink insulating foam.
My sister has a paddle that I don't think is just an oval shaft on top of a round base, I think hers might be built with some sort of rotation pressure pulling the glass to the outside of a female mold.

How do you mold
: that since the ferrule is round and the blades need the shaft to taper.
: The easiest way seems to me to do what most commercial paddles do, by
: adding the oval to the outside of a round shaft, but that increases
: weight. An internal mold won't be extractable so it will have to be light.