GPSes in vehicles is, I believe, defined in their config rather than as an item, so I'm guessing there's no real way or removing it barring a config change.
That said, perhaps you could try showGPS false while inside a vehicle? With a bit of luck that command is more 'universal' than just removing the item. Other than that, yes - some kind of black screen and such might be implementable, but try the above command first.
Wolfrug out.