Here is the answer-
http://www.amazon.com/FLEX-HONE-BRAK...lex+hone+rotor
Faster than emery cloth or scotch brite. Load it up in your drill and go. Make sure to also buy the flex hone oil as it needs lubrication to prevent galling.
And never use sandpaper, as the silicon can impregnate the metal and turn into a carbide when the brakes are used for the first time. Carbides are very very hard and durable. Not good for the rotor surface.
PS, when changing compounds, always either replace the rotors or remove the pad transfer layer using one of the above methods. Flex Hone is the way I like to go because it's fast and effective. Resurfacing isn't preferable since it thins the rotor and exacerbates any thermal issues that might exist.