Channel mixing in mission planner

I’m currently building a fishing bait boat which has a Flysky FS-I6X, Flysky iA10B receiver, Dragonfly Pro 5 sonar, ESP8266, & Pixhawk

I’ve figured out how to get all 10 channels to show up in mission planner using S-BUS (Flysky iA10B has both analog 8ch and digital 10ch S-BUS) using pwm (ppm doesn’t show/work in mission planner for some reason).

However, I have certain channels mixed on the handset. I can’t figure out how to do the channel mixing in mission planner.

The handset and boat are set up as follows:

Ch5 operates the left hopper servo on a toggle switch (SWA) with the end point set to 10%.

Ch10 operates the right hopper servo on another toggle switch (SWD), the end point is also set to 10%.

Ch5 is mixed with Ch9 which operates a relay to change the power source to the leds from constant supply to a flasher unit so the leds flash when the hopper is dropped.

Ch10 is also mixed with Ch9 to do the same as above.

Ch5/Ch9 mix is set up as follows:
Master: Ch5
Slave: Ch9
100% Positive mix
0% Negative mix
+50% Offset

Ch10/Ch9 mix is as follows:
Master: Ch10
Slave: Ch9
100% Positive mix
100% Negative mix
0% Offset

I’d like to be able to do this within mission planner. I’ve looked online and it looks extremely complicated, confusing and convoluted to set up.

If someone can explain in simple terms how its done it’d be a huge help.