The Hoverbucker is a creation of Ronnie Hinton and Daniel Diaz Brauch which started out as a Squier Bullet stratocaster . They took the middle pickup and mounted it over the neck pickup, to give a sound like a humbucker. It is mounted upside down, with the top facing the strings. I don't know what the phase relationship with the neck pickup would be: the middle pickup is usually wound out of phase with the neck, but by mounting it like this the signals from the pickups would be exactly out of phase too.
Not content with the hoverbucker modification they went one step further and mounted a pickup between the bridge and the tailpiece. This picks up the high plinky noises you make when you strum behind the bridge (maybe you could change the pitch by pressing down on the strings in front of the bridge). You can see it in action in the video below, as Daniel gives it a strum. At guitar-list we love this kind of guitar experimentationm there is definetly some mileage in an over-the-strings pickup idea.