Here are several patterns, one for an infinity scarf and the others for braided scarves that could be adapted to infinity designs. (You could do a provisional cast on and then graft or 3-needle bind off the end to the cast on.)
http://www.spudandchloe.com/blog/200...-free-pattern/
http://tlc.howstuffworks.com/home/fr...-patterns5.htm
http://www.ravelry.com/patterns/libr...infinity-scarf