Regarding laying on the ground:
I forgot to mention this - but Sean or Bryan mentioned at one point this lens support that looks like a Frisbee turned upside-down with a ball head on it. I can't for the life of me remember who made it - but it looked like it would be real easy to use laying down and slide easily. They had taken some pretty nice bird photos using it. Also, Kirk makes a lowpod that would work, although you can't slide it very well.