Not directly possible -- but might be achievable by displaying two (or more, in case of horizontal and vertical scrolling) MKMapViews simultaneously when an edge is reached.
That implies building your own view and scroll logic, and to be honest I would be surprised if it is possible to make it work seamlessly.
You might have better luck doing this with a custom set of map tiles.
Just my 2¢. Sounds like an interesting project -- good luck