Turns out the LoL Shield was charlieplexed, which is rather unsuitable for my needs and I really don't wanna spend the extra processing on the debugging tools. I have therefor decided to insert two 8x8 dual-color LED-modules instead, which is even better actually as they work exactly the same as the light-matrix I'm building - simply extend the wires a bit.
I've also figured out it would be nice with a simple and quick push-to-test button. The plan is to step through all lights, column by column when pressed and held down. This allows quick and easy troubleshooting of broken bulbs or chains without having to interface with the menus, and I could do this with the playfield up as well.