sorry I can't help you with a qualified "I have already done that" solution, but here's the direction I would be thinking in:
There's two things which are stupid with the thing, one that the button hurts on your face, the other that the record function does not latch.
connect an external footswitch (of the kind which can be switched between momentary and latching) in parallel to the existing button.
This would require a simple solder job, and a hole in the housing (either leading the footswitch's cable through it, or installing an additional 1/4'' jack).
And I also have a question: do you have a video available which show how you play it with your face?