A small wire wheel on a dremmel. If you dont have a dremmel, put a little wire wheel in a drill.
Drinnling a hole in the moddle of a plug, it it is the correct type of thread, would be the best bet. I would insert a cotter pin prior to installing the plug, and bend the wings from the bottom. As the engine runs, the pin will vibrate and self clean the hole, so it doesnt plug up.