The two ways I've used to do that are either:
* move the player if he exits either end of layout. Scrolling is unbounded and the seam is hidden by either carefully placing objects in the same places on either end or using the paster object to copy the other side. It just to make the transition appear seamless.
* move everything under the player instead of the player. And just wrap the pieces as the leave the layout.
Both those take care of the visual portion. The seam will be a problem with ai and such so you'll have to take that into consideration with your events.
I think the first method makes sense, if unbounded scroll is trigger-able, so when your reach that part of the level it turns bounding off, then you could proceed with the section that wraps. As so matching AI, I don't think either of my examples need that:
Neither have anything that would be different on a wrap, so I think it could be done that way. Would use paster be essential or could it be done with creative triggering?