reoder list on RJS response ( or Prototype method?)

I've got a list of items that I'd like to reorder as part of an RJS response to an Ajax call to the server. Normally I would just place the entire list in a div and redraw the list from a partial, but in this case that's not a viable option.

It seems to me that this sort of thing *should* be possible, since the drag&drop is able to re-order lists. However, I'm having trouble finding the low level Protoype or methods that I can call to do this. I've dug through the source of each as well as the respective API docs, but come up empty handed so far.

It would make me vary happy if all I had to place in my RJS code was something simple like page.update_position('third_list_item',1) or page['third_list_item'].move_to_top, but I'm realizing now that that's probably not possible. If someone with a low level understanding of how either of these libraries work that can point me in the right direction, it would be much appreciated.