European specification COMANDs can be activated to permit watching DVDs. Check with your dealers. Alternatively, search the site using terms like "activation" or "COMAND codes." However, I understand (without knowing for sure) that the codes were not released to do this beginning in the 2006 model year.
You might start here:
Dvd Video Unlock - MBWorld.org Forums - No guarantees any will work. They do not mention the W169.
And I hope you are doing this for your passenger. Watching DVDs from the driver's seat is just insane. Unless you're exploring how well your Benz stands up to a collision.
To avoid an avalanche of questions that have been answered again and again, U.S. specification COMANDs cannot be "unlocked" for video in this way. They lack the circuitry to decode DVD video.