Here's a simple design:
http://www.ehow.com/how_4967135_make...pedal-led.html
If you don't need the LED on/off indicator, then it becomes almost absurdly simple--just wire a stomp switch to make/break the connection between the two jack tips. With no LED, you don't even need to use a stereo jack on the input side.
If it "pops" when operated, just solder a 1M resistor between the tip and sleeve of the input jack. Might also be a good idea to connect the bottom right lug of the switch as drawn to the output jack sleeve, so that the tip is grounded when off.