The guitar patch for Reason 7 that I made (which you can download for free), uses a 'Line 6' amplifier module. This module is equipped with a volume pedal. Using this option gives you control over the 'expression' of the instrument.
In the example to the right you will find that the volume will slowly increase overtime, to give the sound a steadily increasing sharpness and a 'ringing' feel to it.
Next page (wah-wah)