you could go with the easier option of using a cable mounted switch. but i enjoy making mechanisms and creating more work for myself. so i went for creating a rotary switch using a brass knob from a drawer. i threaded a bolt into it and welded a washer off center to touch the switch, the video should explain.
invalid movie: http://www.vimeo.com/5487773
the base can be made out of whatever you want i used wood because it has a nice finish and made it much easier for me to router the shapes to create my switch.