I broke my collarbone back in the summer of '05. (Details here:
Broke my collar bone 2 hrs. ago.)
I don't know about your son, but I couldn't even think about going into the figure 8 harness, I had to just go w/ the sling, more support.
I asked the doctor about supplements and he advised me that one extra calcium pill could help, do not take more than that as it can lead to further complications. Hope this helps.