Only real solution is bring to to a wheel repair shop they dhould be able to fix it and repaint it. Wont be cheap though. I paid 250$ for 1 rim to get redone.
You just answered your own question... knock down high spots with a file, use some filler to fill in any deep gouges/scratches, sand to shape even with contours of the wheel and prep the wheel for paint. Its not exactly rocket science, just average body work.