First post of a south of France (Toulouse) X5 2002 adict...

Perhaps a solution I will test in few days :
As far as the AUX cable is automatically detected because of the resistor between Left and Right cable near AUX input, disabling the CDC, I think, as a matter of fact, that if you "cut" by a manual double switch the left and right cable, the AUX cable would no longer be detected, and CDC would reappear. Placing the microswitch near the AUX input in the glove case would allow to activate it when needed.

This has to be tested...

Hope it will help !