This is a pretty simple hack.
If you want to control the lights, you can put a switch in the middle of the jumper wire, otherwise, with this method the lights will always be on so long as there is power to the keyboard. If you use a powered hub, the lights will remain on even if the computer is off. This is because the traces that go to the controller are not fully populated and without consulting an electronics expert (not me) and maybe using a scope, you probably won't get that working, and that is if it's even built into the controller at all.
All you simply (HA!) need to do is add resistors and LEDs, and then jumper (wire) the ground bypassing the controller.
Here it is partially finished, I was just making sure it works, I'll be doing the rest this weekend.
Necessary items:
68 100ohm SMT resistors
68 3mm diameter 5volt leds
A 2in strip of small wire.
Open the keyboard, there is one screw under each pad and two under the small stickers at top and bottom in the middle. There is nothing under the large label.
First add your jumper wire, this needs to go from the connector over to a pad on the pcb as shown. Ignore the crappy joints, I was tacking things.
Close ups:
Now add your resistors and LEDs.
LEDs need to be installed with the long leg in the + hole, I recommend bending them out 45 degrees after going in to hold them in pace while you solder. Make sure they are in all the way, I had one I had to redo because it hit the keycap.
Resistors are super tiny, but they are not as bad or time consuming to do as you think once you get a rhythm going.
I add a teeny dab of fresh solder to one pad (I did both, bad idea) then while holding the resistor in place with tweezers, melt it down. Now go add solder to the other side.
Next up, finish adding parts and print covers to change color and control the direction of light output.