Also, I'm sure you can find the part number for the switch MB uses. I'd guess its a dumb soft switch, and that means that you can wire it to control whatever you want. However, I can tell you from my experience with my C-class, that Mercedes parts are hella expansive, and you will spend a lot of money and time on the idea of making your switches look factory, versus installing a third party switch box and wiring it to whatever dingus you want to control with the switch.
If MB is using a smart soft switch (i.e. sending a data signal through the CAN BUS rather than a simple current signal), which is possible- this is Mercedes - but unlikely (even most keyboards are dumb soft switches, the data is converted by the keyboards control module, rather than at the switch activation point), then you are SOL on that. I would also guess that there is quite a bit of blank space above the central panels switch bank where you can drill in switches for your own wiring. I haven't taken the thing apart. Working on modern cars, which are basically huge computers, gives me the jitters. When I spent $45k on the thing and hacking apart the wiring would likely void my warranty, it gives me the double jitters.