http://www.amainhobbies.com/product_...Wheel-Balancer
This is the balencer I use. I stick one of my spare hubs into the wheel I'm balenceing then put one of the cones on backwards. Works well. Or you could just by the adapter they recommend.
It doesn't use bearings or magnets, it uses low friction blades. Best balencer out there by far.
I've done 1/10th buggy, truck, and coor wheels and 1/8th buggy and truggy wheels with it.
Tires fom may shift, so I rebalence every once in a while. Haveing a good balencer makes this alot easier than some homemade contraption.