There are many ways to bind off more loosely from using a larger needle to Jeny's Surprisingly Stretchy bind off. http://www.youtube.com/watch?v=53Mtbkyf5CQ
If you do a search you can find others. Undoubtedly one of them will suit your needs. Once I used the Surprisingly Stretchy Bind Off and it was too stretchy so I redid it and as in this case I was binding off ribbing, I only used the yo with the purl stitches.