It won’t be hard to adapt what I have done here with an ESP32 : Open Source French Drone Identification . You will have wifi broadcasting, it will need a new vendor specific number. The takeoff position is set to the first good GPS fix. Simple. No need to be super accurate.
The only pain will be to have the UA to check the RID is active… So mostly use a GPIO to check if it is ok will be the simpler solution. No, need for complex protocol.