I bought the PVP12 pedal and made a cable with stereo jack plug for KN side and two mono jack plugs for pedal side. This works fine exept that volume decreases when pedal is depressed. After modifying the potmeter connections in the pedal this was solved. It is not necessary to modify the potentiometer (100kOhm, not 200kOhm as mentioned before) because the volume transition is smoothly.
Thanks for you advise Bill.
Bert