Instructables user Nano_Burger has found a creative way to repurpose an old laptop bag's padded sling into a camera strap. It involves cutting out strips of nylon and fashioning them into loops for your camera strap lugs.
The creator uses a no-sew method that he calls "steel reinforced adhesive," which involves gluing the material with epoxy and then securing it with staples. If you're afraid it won't hold, he advises a strip of black tape for added security. After the glue has dried, all you need to do is clip both ends of the laptop strap, and voila, you've got yourself a camera strap.
If this little project is something you'd like to attempt, head over to his site for more detailed instructions.