"B" is hardly used at all (I wish it had a better use) as far as I've seen. The GPS Lock LED (C) is easily replicated externally, try searching for something like "remote status LED" here, there is lots of good info, it's easier than ever to do with the latest version(s) of Mission Planner. It basically follows the LED on the GPS board, and that shouldn't be buried deep anyway. "A" is usefully/functionally replicated by an Armed/Disarmed LED, also described in the suggested search articles. A and C are the very important ones. Hope this helps, it is actually pretty easy to do so don't be "intimidated" if it sounds complicated at first.
I replicated the LEDs also using a driver chip (that I had installed already for something else) so I could use 12V LEDs, and these are almost blindingly bright indoors, and are quite visible from a decent distance even in bright sunlight. Overkill, but a bit of comfort (I don't have telemetry) as well as an orientation aid in daylight as I mounted them on the "back" of my quad.
I can't seem to find the the post, but you can simple modify your code and use any of the existing outputs on your APM to extend the lights.
If you don't want to change anything in the code then this is the best thread for you:
Check comments for interesting additions.
Thank you for your reply. This was very helpfull.