Disclosure: I have not done his before.
I guess my approach to this would to treat it like a "hand-wired" project.
1. Remove the existing controller (40-pin, lop left of the PBC) and replace it with a socket
2. Map put which pins are for the rows, which for the columns, and for now ignore the LEDs
3. Given the required # of rows and columns (sum=rows+columns) will tell you the minimum number of IO pins your controller needs.
Looks like you have 100 keys, so 10 rows + 10 columns or 20 IO pins is the least it could be configured for, but more likely it's
something like 5-6 rows * 20 columns requiring 25 or 26 IO pins needed
4. Get a capable controller (Teensy perhaps? with enough pins. Summary here:
https://www.pjrc.com/teensy/pinout.html) or maybe you can use the soarer?
5. Configure QMK or TMK to set the row and column pins used
6. Add the key-map
7. Cross-connect the needed Teensy pins to the existing controller socket. Don't connect anything other than the keyboard scan matrix.
Later, maybe, try to add the LEDs too.
It's a bit of work, but should be possible.
All the beast.
