You remove rust by wearing away the surface in which it resides. So some scratching is inevitable. But, removing surface rust should leave minimal damage. Start by wiping the surface down with a good coat of light oil (baby oil works fine), this will actually remove some of the loose discoloration. Dry off the blade and work the surface with a rust eraser (just like a pencil eraser), it's a small hard rubber block imbedded with diamond dust, available from AG Russel and most knife shops. You can then wipe it down with a metal polish (look at the local auto parts shop) to remove any remaining traces of rust.
n2s