I think your only option would be finding the whole unit out of a Rubi and wiring one of the buttons to what you want it to do.
will be easier and cheaper to just put a switch somewhere else.
Hopefully AlecW will read this post and post a pic. If you don't want to buy a switch panel you can add switches to the empty spot between the vents like he did. IO think it is the best looking job I have seen without adding a panel