Trainer PPM input - mix with trainer control?

Searches didn't turn up anything, and a vague perusal of the available options didn't get me anywhere...
I'm looking into buddy-boxing with my 5yo son, him with a 7E, me with a 6S. From what I can see, you can either hand control of certain sticks, or certain channels, fully over to the trainee. My question is, can you mix the trainee's inputs into the trainer's? Perhaps something that is being done with the "extra inputs" scene?
I'm thinking something along the lines of giving me 100% scaling on my inputs, but any stick inputs (say just rudder and elevator) coming from him would be scaled down to maybe 30%, and only when a certain switch is on? So he can madly mash away at the sticks and get some sort of response, but I'm the one mostly in control?
I don't know if it's something I've overlooked or whether it's just not available. A mix type under complex mixer?

I've been going through the menus, can anyone confirm what happens here;
- in Model Setup, if "PPM In" is set to "stick", does that turn the trainee's stick inputs into PPM1, PPM2, PPM3, PPM4? If so, is there a specified order or is it just trial and error?
- if the above, in the Complex Mixer can you then mix in a "Src" of "PPM1" for example as a mix of the trainee's throttle inputs, to Add/Multiply/Replace the Thr source?

In stick mode, each stick on the slave matches up to a stick on the Master. This allows you to control the mix results in the model.ini on the Master. You set the relationship of the ppm channel to your stick by clicking on the Stick entry in the PPM In button. The defaults are laid out in Chapter 11 of the User Guide.
Since the mixing is done on the Master, you can mix in the PPM source just like any other SRC. I see the PPM channels in the Switch button for Complex mixer, too. I haven't done the mixing from a slave TX, but it seems like it's just like what we do when we add buttons and switches.

This is a cool feature, and I'd appreciate you sharing your experiences when you get this working!

Can't find the info anywhere; does a non-deviated stock 7E output PPM at all times or do you need to do something special? Also, will a stereo cable work or only mono? I saw some discussions on stereo cables on the extra inputs thread but don't know what the stock setup requires

I don't know how the stock software deals with the trainer port.

I do know the connector. The connector for the trainer port uses only the tip and shield of the 1/8" plug, so you can use a mono or stereo cable. If you use a stereo cable, the ring before the shield is shorted to the shield when the cable is inserted, so in effect you get a mono cable.