What about a strong, alternating magnetic field such as that which might be generated by a rotating drum with magnets fixed to its surface in alternate N-S-N-S fashion?
You can use this technique to REPEL copper, aluminum and other non-ferromagnetic metals. It's the eddy currents which cause the repulsion.
This is how trash recycling machines separate ferromagnetic metals, non-ferromagnetic metals and paper/plastic/trash. First, they use a magnet to suck up the steel and iron. Then they use a rotating drum magnet to repel the copper, aluminum, etc. into a chute.
Would this technique work in our case?