By passing rc_channel for gimbal

I want to by passing rc channel 9~16 for gimbal camera…
I add set_override call function on GCS_Mavlink.cpp
but it can’t passing the rc input…
if It isn’t possible using channel 9~16, how can i send by passing rc channel signal…??
is there a good examples??
Help me please…

SERVO9_FUNCTION = 1
etc.
etc.

https://www.rcgroups.com/forums/showthread.php?2852885-Controlling-external-devices-like-Gimbals-and-Lights-with-a-Pixhawk