On first glance it appears not possible to add a button to the oem switch module, but a little work with dremel it can be done.
Can't go through the back due to pcb but there is room on top to make access.

 

ejecto seato?

 

Are you attempting to add a fog light switch?

 

It's a remote mute button for escort radar detector. I use a blendmount and like it snugged up under the mirror, can't reach the mute button.

 

Can you send me the SPEC or link to the mounting bracket you used?
I had one for my G37, but it does not fit my RX 350
Thanks

 

Great idea. I need to do this for my fog light kit.

 

It's a https://blendmount.com/ you have to put in your vehicle model and detector model.
Mine is for a 3rd Gen IS but been able to make it work on 2 successive Lexus by purchasing an add-on piece.