Pete:
What is the picture telling us? What are we supposed to be paying attention to?
Look where and how the trap line attaches to the harness. I appears to be a small line that goes from the hook to the shoulder straps. The attachment point seems to slide along that line.
<img src="http://www.catsailor.com/forums/images/graemlins/blush.gif" alt="" /> On second glance, that is just the trap bungy! Still, I think I'll try to cobble something together.