I was going back thought the old MG files this morning, trying to avoid the 120 degree F (49 degrees C!) heat here in Arizona, and found this one from one of the MG teachers at HQ, Jon Valentine.
See here:
http://www.drillsandskills.com/article/17
We do not have the luxury of those huge padded blocks, so have to make do with a spotter, or by lowering the rings. A side note: we have found that the "skin the dog" (our version of the popular stretch/strength move that is also called the German hang) can be an excellent shoulder rehab exercise.
The key is using the move this way is to either lower the rings so that you (if working solo) can control the depth you lower to or, better IMO, have someone stand behind you and as soon as they go over the balance point, you take their feet—this way they are in 100% control of how much force the shoulders experience.
A second key factor in making this move effective rehab is that you ask the person on the rings to gently actively lift themselves from the lowest point they can get to back up to the balance point. You assist by lifting the feet. In the beginning, make sure you do most of the work!
I will be very interested in people's responses to using this move in this fashion. KL