no one said you can't do it..... but unless you have stolen one with split screen to take the very expensive parts from, and have a skilled mate with a hooky version of Xentry then you won't get far

a sensible price (all in with parts) drive in drive out fitting second hand components and not vandalising the car, should start from $1200 and if they gave you good parts, a warranty and were professionals you should expect it to be closer to $2000

As others have said, the systems in a modern vehicle are completely interconnected. The COMAND processor unit is different, and has different software on it to support the SPLITVIEW feature. The wiring is likely different making this more than just a plug/play wire harness modification. I know for fact that the video connector on the back of facelifted vehicles is different from older cars (as an example).

There is also no documented factory procedure for retrofitting on older cars. Adding SPLITVIEW to a facelift vehicle is something that is documented in the Mercedes WIS (Workshop Information System).

The misconfiguration of a newer COMAND processor communicating with other modules that do not expect it would likely cause all sorts of errors and malfunctions that are difficult to predict.

As BOTUS said, it's not "impossible" given enough time and money, but unlike say the VW/Audi or BMW forums, there is very little information on this type of retrofit on older vehicles.