The E39 has an option for a rear mounted can fridge. It is finished exactly the same as the rest of the interior with matching wood trim and goes between the rear seat and the center console (on top of the hump). It's a real fridge and is shaped to hold 2 cans and 2 cans only. When closed, it just looks like an extension of the center console (albeit nicer cause it's finished in wood, not leather or pleather)

The only other BMW that I know of that has the fridge is the E65/66. It has a champagne cooler in the trunk with access through what would be the ski pass through/center armrest.