The tracks have been designed into the boards on the Mk2. It is not a hack; the problem was in obtaining 3.5 mm White LEDs, as only 5mm ones were available at the time of design. You could fit LEDs yourself without effort.

When the guys looked at button illumination, it looked a bit tacky and could not really decide. They did have transparent buttons cast up to try it, but they were only for test.

Note that the tracking is not present in the Mk1 display boards, so you would have to hack this.

Me, I'm just waiting till the guarantee expires before going in with the soldering iron and 3.5 blue LEDs. Now where's my hobby casting kit...