Unlinking heated side mirrors / rear defrost

[Alezius]

I have a 2009 5doors LB. it comes with heated side mirrors.
To activate it, you push on the rear defrost button.

I'd like to activate heated mirrors with a separate switch.
I use the mirrors heater when it rains... don't need the rear defrost in summer...
Plus, the defroster is on a timer and don't need that on the mirrors.

Does somebody have the 2009 EWD?
(or anyone have done this or know how to do it?)

if never been done, i might consider makin' a How-to.

thanks.