I added a "Super Switch" to switch in and out of circuit a larger capacitor that lowers the frequency range of the wah into the bass region. A second Super Switch switches the wah-wah in and out of bypass -- sometimes I like the sound of the resonant filter but don't want to hear the sweep; by tapping the momentary switch I can momentarily punch the filter out while changing frequency. There's a power switch in the upper right corner, so I can leave the circuit patched without draining the battery. I couldn't find a box exactly the width of the pedal, so I added a second jack for output (lower left corner in photo of the circuit's interior.)
Great information on wah-wah theory and mods can be found here.
(Scroll down for all three photos.)