Quoted from herg:

I have done some work on GI for WPC machines, including creating a prototype board that does pretty much what PT says. It converts AC to DC, then uses PWM to power the GI. I have the PC software written to control and program it, and I can manually control the brightness of each GI string.
The issues I still have are getting rid of all the heat that is generated, monitoring the signalling to automatically control the brightness levels, then trying to make it all physically fit in the backbox and still be affordable. I'm not sure if it will ever be practical due to all of these issues.