What kind of casing is it housed in? With some metal casings, you could just stick the computer in a warm acid bath (HCL would work well) for a day or two. Cover the scratch with an inert material to the particular acid, and the areas around the scratch will be eaten down until level. Your computer will even be lighter as a result!
If you plan on performing this procedure, please send cash or money order in advance. Pre-pay only.
Lemme know how it goes! Good luck! Jesus loves you!