Have you tried the old ibus interfaces that were used with the E38/E39?

Maybe they won't work because the required button is not present on the X3?

All you need to do is send an ibus command to switch video mode whilst not changing audio mode.

To do that you need a little microcontroller (like a PIC) that listens for the special button press, then sends the video switch command

Easy if you know how to build and program microcontrollers...