This is the tutorial I made for an spanish web:
http://portal.batacas.com/index.php?vie ... &Itemid=74
(it is roland style three zones, but it can be converted easily to yamaha style) I post it so you can see a bell switch is easy to do.
There is another guy who, based on my tutorial, made its own bell switch, I think it is also very functional:
http://www.batacas.com/foros/showthread.php?t=41402
You can see here a video showing how good they trigger (bell, edge and choke):
http://www.youtube.com/watch?v=zplaNW9N ... 402&page=2