Russell, the slot is pretty small, about 5/8" long on each side. I don't know how much of a chaser I can fit. I am thinking more along the lines of two different colored LED's slowly pulsing in a somewhat random pattern. I'm trying to get some ideas of what to add, I might use one of the Arduino Nano boards I have as a simple way to do this task.
If you have the original Phantom, you can see the slots near the rear top, they are part of the plastic for the rear light and shell posts. I guess they thought the anemic backup light would shine when it was on, bad read, it doesn't! 
