Bungee launch fail without GPS: motor doesn't start

I’m testing bungee launch in SITL / XPlane and it works fine when SIM_GPS_DISABLE is 0;
When SIM_GPS_DISABLE is 1, motor doesn’t get triggered by TKOFF_THR_MINACC

fail.bin (540 KB)

I have continued experimenting.
It seems ground speed is mandatory for the motor to get started even when no GPS is set in EKF settings.
Any ideas what could be done about that except custom firmware?

Update: it won’t work since there is a check and GPS required

/*   Check for automatic takeoff conditions being met using the following sequence:
 *   1) Check for adequate GPS lock - if not return false
 *   2) Check the gravity compensated longitudinal acceleration against the threshold and start the timer if true
 *   3) Wait until the timer has reached the specified value (increments of 0.1 sec) and then check the GPS speed against the threshold
 *   4) If the GPS speed is above the threshold and the attitude is within limits then return true and reset the timer
 *   5) If the GPS speed and attitude within limits has not been achieved after 2.5 seconds, return false and reset the timer
 *   6) If the time lapsed since the last timecheck is greater than 0.2 seconds, return false and reset the timer
 *   NOTE : This function relies on the TECS 50Hz processing for its acceleration measure.
bool Plane::auto_takeoff_check(void)