Richard,

Take a look at the www.balancemasters.com website. They do not sell
balancing machines for balancing whatever. They sell a product that
attaches permanently to the prop or other wheels - big 18 wheeler
trucks are using them - and automaically provides balance to the
rotating disc. It is a unique device that has a ringed tube of mercury
and the motion of mercury provides live balance to a rotating object.

If anybody has used one of these things on their prop please let us
know what success you had.