Probably a lot harder then in the old SLK. There it was simple, turn a piece of metal and pull hard.
The new one seems to have the knob almost completely encased in leather, except for a small bit in the middle. Maybe this is the point where one can separate the top part from the bottom one.
Seeing as lifting this piece of the central area is really simple by just placing your hand inside the leather pouch area of the shifter, and unlocking it via a press of a clip within, maybe there's a similar 'clip' procedure to the shifter.
If anyone knows, please post the results, as I too am interested, in case I ever decide to do my mod with the starter button on the shifter [
] (maybe I'll be asking a dealer next week when I take a few days off to visit the Geneva car show... my dealer gave me two free tickets to it, WOOT!!!)