Control late model Head Unit volume with Original Radio Knob?
 

I would like to Control a double DIN head unit (in the glovebox) volume with Original Radio Knob? I have a 70 GMC LWB. I have a GM radio on the way. It will basically be a hole filler so the dash looks correct. But I thought it would be cool if the volume knob controlled a head unit I plan on installing in the glovebox. Maybe even have the push buttons operate other stereo functions.

I was thinking of using a Raspberry Pi or arduino board to do the work. Just not sure if it has been done before and maybe it would save me a bunch of work.

Has anyone done this?