I used a LED/LDR instead of a pot. There's a lever inside that blocks or unblocks light as you step on it. It works great too.
http://www.logmonster.com/images/full/?pic=d007d_1160300734-422-13888.jpg
http://www.logmonster.com/images/full/?pic=d007d_1160300734-422-13888.jpg