Reply to LEDs in the preset buttons of MFPros: question

The preset buttons on the MidiFighter Pros seem to have LEDs to indicate which preset is currently active.

I know the MidiFighter expansion slots allow for the 4 buttons via the digital slots. The question is, what was done extra on the Pros to allow the LEDs to function? And how easily is that to duplicate when adding controls to a MidiFighter Classic?

as always, big thanks!
_k