I don't know about C7.5, but windows down & up / sunroof open & close via key fob is possible with OBD-II on C7 and prior.

Here's a YouTube that may be helpful: https://www.youtube.com/watch?v=zy9NFw5Wo3I

NOTE: I have noticed that the key fob range is very limited for this function, meaning that I have to be standing no more than, say, 12-15 ft away from vehicle for it to work. Thus, I really don't use it very much at all.