The problem is that by VIN number, his key will only work in the door. If I am correct, he has the original cut for the doors, and a new cut for the ignition. No idea if MB "knows" the new cut he has for the ignition.
I believe there are a few places that can just do a duplicate on this complex style of key, no idea how you go about locating such a place.
The "right" thing to do would be to order and install the correct lock cylinder for the car, it's not that bad of a job to do just the cylinder, and it'll come with a new (correct) key