if you go look at "led light base" for pedals... sm concept will work. I've done this a number of time (for pedals). Take an led and sand the top of it flat and right up to the contacts. Then use a clear pickguard, put some design/sticker on the back side of it... everywhere but where the led will be glued to it. This will make the light only go out the sides.
Leds go thru batteries fast... so you'll want to use the biggest resistor possible - just test it out. with a water clear led you could probably go 12k. also, might want to put in a push/pull switch so you can turn it off.
(probably place the led right under the knobs so it doesn't shine right where the led is)