When designing your level, just make a "bridge" section, like this:
XY|ABCD|XY
"ABCD" is your level. "XY" is the bridge part. The "| |" is the screen. When the player gets to the left:
|XY|ABCDXY
You teleport them to the right:
XYABCD|XY|
But because the map looks the same, they won't even notice! ;) The only thing to remember is to never put enemies or action objects on the "bridge", else they will notice. ;)