This is something I've been looking into since I'd love to do it with one of my 60% keyboards. Fortunately, with a Filco, it's even easier than the 60% boards I've been looking at.
Assuming that
this will fit in the case below the PCB, the easiest way is probably to get a cable kit (I know pexon has some) or research and buy the stuff yourself from Mouser so you can wire an internal cable and run it to the linked adaptor. Then find a battery that will fit in the case and plug it into the adapter. Do that and you'll be good to go.
The more technically minded way would be to get an Arduino (or a Teensy if it's compatible) and a
bluetooth controller and wire it in the case. This will also require a battery. It's more complicated and well outside my technical know how.
