If you're lucky, you can get a flathead screwdriver into the seam / joint of the clamp and get it to open. Cutting it is easier, in my opinion. In any case, those BMW clamps are one-time use only. I'm still awake so feel free to text me if you are attempting anything now!
There are some suggestions here: http://www.e90post.com/forums/showthread.php?t=278126