Just a few other things to think about. I originally was going to use some slow color changing LEDs from superbrightleds.com. They changed colors every 4 seconds which I think would be very cool, but I wasn't sure if they would stay in sync with eachother so I ended up using just red. This vid gives you an idea of the effect... http://www.youtube.com/watch?v=DDQfz0ElFQ4
Also, I considered just using one LED in the little space in between the two cupholders and just letting it stick up since nothing would be sitting directly on top of it. This would be a good place to use an actual LED holder of some sort. My concern here though was if it would actually make a bottle light up as well if it wasn't directly under it. I would use a wide angle LED if I were to do this.
I would be intersted in seeing anyone's results if you try either of these ideas, or whatever else you come up with.