SMD LED soldered onto the bottom of the through hole pads.
Blue doesn't work that well when passing through orange acrylic but it's very visible for the bottom half of the acrylic plate.
I will also consider taking on soldering jobs if there's a decent amount of interest for me to get my own soldering iron (instead of constantly borrowing one) which means I would also have to order switches too for those who want it soldered. Anyway, that's another story.
I got detailed instructions from GFW about creating the firmware without TMK so I'll try that this weekend and hopefully have the GB running next week with payment collection by the 21st of January.