Corncobs, where did you end up placing the LED in the cup holders? Beneath the rear spring clip in the cup holder?
Yes right below the opening for the spring clamp. Let me know if you need a closer picture that shows it better.
The wire for the LEDs is paper thin so it doesn't interfere with the operation at all. Also the LED itself is so thin that's not in the way for any cup or bottle.
I found it a bit tricky to get them to stick to the plastic. It's really odd silky smooth plastic the 3M molding tape was fine for a while but I ended up fixing it with a drop a crazy clue.
Tapping into the existing wires should be fine. They also sell RGB LED of the same format IIRC so it might even be possible to have them color changing. Question would be if the control signal are the same?