Glow powder mixed with clear epoxy (2 part fast setting) ...applied in the depressions, with a toothpick... I did this to some of my builds. (Not saying that's what these are...just a possibility)
Also epoxy could be put in small vials.
A few low power led's should be able to accomplish this no problem. For all of you that say size is an issue, led's can be made thinner than a penny and about 2mm across. Size is not an issue here. The only issue I can think of would be that WL probably won't include an option to turn the led's off. Of course they could always use glow strips, but that's really not very cool.