I haven't seen any of the videos. I'd assume that there's some creative use of a camera to give the illusion that no one is behind the wheel.

After all, in the the "two girls one cup" video the girls eat chocolate ice cream. There was a camera cut between filling the cone (with something that is not ice cream) and the girls eating from the cone. It's clear that in the cut when the girls are eating from the cone, the brown runny soft soft substance is chocolate ice cream. Your imagination fills in that it was the "not ice cream" from the first shot.

Edit: You must have added the link while I wrote the above comment.