They've done it since the dawn of time. There's still a few test mules of the early girls getting around. But they wouldn't necessarily cover up the bumper...
I think the 'wallpaper' just attracts attention rather than actually camouflages anything. Would average Joe look twice if it just looked like a white GTS on a trailer? Seems more like a marketing attempt to get the juices flowing. Half wrap up a car and drive it around town for a few hours to get some people talking.