You need the W220 CD stacker harness and you should expect that it will mount in left rear void near the left stop lamp.
The mounting bracket can probably be the W208 type .
Since the W220 is very long you will have no problems with cable length. Optical cabling will be a small problem. You will need to special order some lengths. All this would be slightly easier if you have voice control or phone prewired. Then at least the optical feed is closer.
It would cost so much money to do this that you would be better off with a COMAND and an iPOD through the AUX audio port.