Adjust passenger seat from driver side
 

I can adjust the passenger seat using the driver seat controls when the car is stationary. However, if I try to do that when driving, I get an error message informing me that this function is only available when the car is stationary.

The need for me to do this is usually on a longer trip on the highway when I have a passenger incapable of operating the seat controls and it is really inconvenient for me to pull over and stop the car.

Would anyone know if there is a VAG-com setting to make this either always operable while driving (like the VIM mod) or to have an override for the warning, like the navigation entry commands do?

Please clarify - how are you adjusting the passenger seat from the driver's side?
Are you talking about some controls via the MMI or the actual seating position?

Adjust passenger seat from driver side
 

You do this by first pressing the "CAR" button, after which on the MMI screen you go:

Car Systems => Vehicle Settings => Seats => Passenger Seat => Adjust Seat Position

At this step the screen reads: "The passenger seat can now be adjusted using the controls for the driver seat".

And yes, you can as long as the vehicle is stationary! And that is what I would like to change.

Do you have memory seat on the passenger side also?

Mine is 2016 RS7,with sport seats, only memory seat on the drivers side. No option in MMI to adjust passenger seat position.

Yes, both sides have independent memory settings. Also ventilation and massage functions on both sides.