My MLP4DSM came today and I had instant success!
I found out that the 5th channel is the push button of the pitch/roll stick and channel 6 is the push button of the throttle/yaw stick.
Now I assigned
CAM Trig = 15
Gimbal Tilt = 16
(to get them out of the way)
Flight Mode = 6 (left push stick)
Home Action = 5 (right push stick)
Since the right push button only has an on/off function it has a default value of 680 which triggers "set home position".
If I push it switches to RTH.
Pushing the left stick and holding it for a second or two would then trigger a mission, which is useless if you don´t have waypoints.
So when I arm, it sets the home position and I should be able to perform RTH. In theory ... haven´t tried in real life.
Hopefully will find some time today.
You only have to keep in mind that pushing the right stick again will set a new home position.
Sadly if I swap channels 5 & 6 the throw of the Yaw channel is limited to +/-400 so I can´t arm.
Will try RTH later if time and weather permits and report back.
Will also do a short write up for the Wiki then...
The red LED on the Tx is a good indicator for the mode: it´s solid in "set home" position and it starts to blink once RTH is triggered.