I took some Stretch Magic, bead and jewelry cord, twice the length that I ultimately wanted, and threaded it through a jump loop. Each end of the Stretch Magic threads through one side of the numbered bead, alternating sides as each bead goes on. I hope this makes sense. Think of a figure eight.
As each row gets knitted, you slide one bead down. Here's where I got the idea for that: http://www.youtube.com/watch?v=cn475adfGgg