VTOL QctaQuad Motor Ordering

Hey there,
I´m currently flying a quadplane setup with four quad and a single tradtional plane motor for forward thrust. I´m using a CUAV V5+ as a flightcontroller.

I´m thinking about upgrading the four quad motors into dual coaxial motors like this one from T-Motor. Something like this one here: https://store-en.tmotor.com/goods.php?id=812

The CUAV V5+ has 14 output channels with 8 being “officially” called motoroutputs M1 to M8.
In my new setup I would have a total of 9 motors though. Is this a problem or can I just use one of the other channels as a motoroutput?

On the QuadPlane wiki of ardupilot (https://ardupilot.org/plane/docs/quadplane-frame-setup.html) it says that the usal motor ordering for this would be from Output 5 to 12. Where is the last (thrust) motor connected?

I´m reluctant to use manual channel mappings via the SERVOn_FUNCTION.

Can anyone with some expierience please give me some hints?

Thanks
Marc

Wouldn’t configuring the Throttle Output to Aux 5 (chan 13) do it? Servo13_FUNCTION to 70