I have problems with foot numbness during non-cycling activities that at least in part from pressure along the tendon running down the foot (it's just inside of the midline of the foot and you can probably feel it if you flex your toes back). I wear orthotics that specifically have a bit of an indentation down them so I don't get too much pressure there (this might be more common in people with flat feet like myself). A stock orthotic that already has an indentation like that, or creating a cut out along there might help. Please don't get mad at me possible podiatrists out there! - you might want to go talk to one to check this out if the common shoe/pedal/clip fixes aren't working