Something else he might try is to have an arranger, and hook MIDI bass pedals into it, then use them in One-Finger mode (so two notes - or feet! - can create most chords he needs). Kind of like what he was doing with his headstock, except with his feet.

Maybe an older Roland RA-90 (or similar) module if he doesn't want to lug around a keyboard and a set of PK-5 bass pedals. Just make sure they are polyphonic, not monophonic pedal triggers. Alternatively, if it is polyphonic (I'm not sure, right now), Roland make a Midi foot controller, the FC200, that can send midi notes. Maybe that is cheaper.....?

Or, even more off the wall, I once saw a OMB guitarist using a set of bass pedals (custom made, probably) that was all buttons, laid out in a grid just like a bass guitar's neck, so hand's and feet were doing essentially the same thing. Very clever......