I'm specifically wondering about some type of movement like the OS resets that specifically targets all the muscles around the scapula (like rowing probably would). You've got me wondering if I can do some kind of straight-arm lever motion... I just dropped down to the floor and was rocking back and forth in a crab-walk position, trying to hold a lever as i moved away from my hands and it felt really promising!
If rowing is the motion you're thinking of, I wouldn't try to fit a square peg into a round hole by trying to accomplish the same thing with a ground based movement. I would just do some kind of rowing or pulling. If the line of thinking around this kind of training is something akin to "natural movements," well, hanging and climbing are natural. I'd just do that.
In regards to ground based moves that would work the back, I'd say you have the right idea. Here's some more ideas:
You could mess with AG walks, but until you've done them for a while they are not easy or gentle.
Easier to harder:
-crab walks with hips down
-crab walks with hips up
-AG walks
-Beyond those I would just progress to L sits, V sits, and...
-manna wall slides (a google will turn up a few videos). Make sure you have some decent shoulder extension and wrist strength first. AG walks and L sit work would lead up to this.
Where I'm lacking is the pull, though. I'm finding it really hard to work my back (rhomboids/traps/rear delts moreso than lats) with this approach and I'd really love to find a way to apply this approach to that part of the back because the strength gains I'm seeing are just that good. Everything I know of that can be done in a high-rep, gentle kind of OS way merely hits the back in an incidental way instead of making it the focus of the activity.
Yeah that's where I would just get off the ground and do hanging and rowing. You can always regress calisthenics movements to make them more "gentle" and higher rep. You could always do a "natural" movement by tying a long rope to something heavy and dragging it in. Tim Anderson wrote about that in one of his books (
Becoming Bulletproof Project if I am not mistaken). The workout consists of something like:
Tie a rope to a heavy object that will slide. Drag it towards you using only your arms. Push it back to where it started. Crawl back to where you started. Repeat.