Got my hands on my GRX shifter, and managed to non-destructively break it down to get the Di2 stuff out of it. Now I just need to take off the last piece from the lever but need my mini torx set from the office tomorrow for that.
At the same time if anyone needs a right hand side ST-RX815 grx di2 lever for parts, let me know, its yours. It leaks oil after a crash, but the body is intact, and all other small parts on it, including lever and the rubber hood.
I also sold my BMC frame to a friend of @hma, and it will be roaming the streets of Budapest, putting the "fast" in fast food :D