Calibrating ESC's without RC


Hi guys!

I’m building a Raspberry Pi drone using RadioLink Crossflight flight controller without RC telemetry. Telemetry is currently via Drone -> -> RPi (wifi) -> mavproxy -> GCS, and it works fine.
I have calibrated the compass, connected the GPS, and all ESCs & motors. The drone seems to be connected correctly.

Instead of RC controller i have connected by wire a PS4 joystick to the pc (gcs). I have calibrated it as RC and it looks fine when tested.

My issue is with calibrating the esc’s.
After I unplug the battery, the FC switches to calibration state when replugged. So when I try to reconnect to the GCS by direct usb (pc usb -> FC usb-c) / RPi mavproxy (RPi usb -> FC usb-c), I get timed out.
It’s like the FC rejects any attempts to connect if in calibration state. this is a paradox because I cant put full throttle without the GCS connection.

The regular way to calibrate the esc’s is to do so with receiver and transmitter.
I thought maybe I should connect the RPi to the FC by the TELEM input (currently its the usb-c).
What you guys think?