I doubt this is a feature you can retrofit into the Murano, since the heating element is within the steering wheel itself. I suppose you can get yourself a Maxima steering wheel (its the same size wheel and design) and custom wire up the heated switch yourself.
My eyes are messed up from reading the SM schematics.:bonk:
Well, I would install a relay fused through the ignition start and run power and sensed through the driver side heated seat switch. Since there are two positions on this switch, you would have to AND the switches - diode.
Also, the SM clearly shows the heated mirrors are energized when the REAR defroster switch is set.