Also Cathy McGinnis of Soaping101 has a youtube video of her version. She uses a chunk of fat drinking straw to create a hole in the soap, removes the straw when unmolding the soap, and threads a rope through the resulting hole. The soap is poured into individual molds, but you could do the same thing with a slab mold if you knew where your cuts were going to be to make the individual bars. I think she showed this idea when making a dog soap, so that's what you would want to look for when finding this video on youtube.
Ah, I ~think~ this is the one: [ame]http://www.youtube.com/watch?v=rN62bLJ8tyo[/ame]