I'd be tempted to treat it like body work on a car: Fill, sand and paint.
Something like JB Weld or perhaps even Bondo to level the inscription back to the same height as the surface of the case, sand it smooth then paint it over. Obviously you'll mask the Apple logo on the back.
It may take some experimentation, but my guess is you can probably find something pretty close to the original color. Since you'll be repainting the entire top you don't have to be 100% on the match, just close enough that the edges won't show a jarring difference between the top and bottom case when it's closed.