I've done it, I asked someone to film me while I did my thing. Be aware that it is never going to be as natural as you do it when you don't a camera pointing at you, it never will. You can't shake the idea of having a camera pointing at you.
My best advice is to go a place where you hace space to move, better if you do it in the street and never mind about the result. You are going to feel weird when you see yourself.
This is a video of me sarging in London, I only had 20 minutes to record this video. Take your time and do lots of approaches.
http://www.youtube.com/watch?v=mpcwRDDh-nI&feature=plcp
Good luck!