great, but my banisters are not round, rather egg shaped, and the flat
end is on the bottom so that it is attached to the railing.

The easiest way I see to get this done would be to build an end piece
which I would use to mount on a drill.
I was thinking of finding an old coke bottle, cutting it in the
center, and putting a roofing nail in the short end.
Then pouring concrete into it, and stuffing in a old tennis ball until
it sets.
Then put this on a drill and using it as a circular file.