I've been there - to prolly all the hacks for this pedal.
Here's one of the best of them:::
http://www.diyguitarist.com/DIYStompboxes/WahMod.htm
Here's the one place where I bet you are going to change a cap:::
However - none of them state they can be used for a bass guitar.
You can pump the bass up and move the transition to a slightly lower place, but frankly, I don't see where it makes the unit RESPOND to E-strings or low notes.
That whole area on the Wah is very weak in rendering bass notes and I don't mind swapping the HIGHs out of it if the response envelope could be sent to Bassland.
So far - I don't see that statement made.