The whole thing is just retarded. Making people pledge and mention God when they don't necessarily believe in it is crazy, and forcing people to is even worse.
For non religious kids, it would be like forcing them to write letters to Santa even when they don't believe anymore
I have no idea how open your teachers are (guessing not much), but maybe you could explain to them why you don't want to stand? I would think that any open-minded person would understand why you don't want to do it, if you have good reasons. But again... most are not.