I use the expression pedal for that. Put a volume pedal after the amp set min ~ 75 max ~95% For some reason going to 100% in my patches sound a bit too brittle. You can also assign the expression pedal to do all sorts of other things.. Amp eq, gain, delay mix, just about any paramater can be adjusted. You can still use the toe switch and the other expression channel for the wha it will be at your lead volume. I gave up on the hd wha's and use my own. If you must have a switch there is a diy box I've seen that uses the 2nd expression input that would allow you toggle between two settings.