AWESOME! I'm inspired to find a neighbor with a treadmill right about now. From the video it appears that the treadmill is slanted very slightly to the right, maybe you could try propping it up a little bit to help keep the slinky center.
BTW, the website that you used was very cluttered with adds. In the future use something cleaner like
http://www.yousendit.com/ which supports 1GB files and no adds, and then just post the file link. It works pretty well.
Thank for posting the video. I'm thinking very happy slinky thoughts right now
