Retrofitting XC60 Heated/Ventilated/Massage Seats Into an XC40?

[leandro.vitali]

I know that they are being controlled by LIN, but the CEM add the ventilation option on the screen, how is it otherwise possible to start ventilation? Massage is controlled by a physical button on the seat.

It's not the CEM adding that option. It's the IHU. 
Screen is connected to the IHU. CEM pushes the config to the IHU and CCM. IHU enables the options on the screen based on the config message came from CEM via FlexRay. 
When user turns on the ventilated or heated front seats, 
Screen sends a message to the IHU. 
IHU sends message to CEM via FlexRay 
CEM sends message to CCM via CAN BUS.

My biggest concern is really related to the distance between the tracks, whether the size was compatible. I believe the hardware would only involve programming and adjusting the wires in the harness.