Personally I would try giving a deep rub along the body to see if the shed can be loosened up. Hopefully that would not stress him out too much. If you see it separate, you'll see it come loose, then you could try rubbing around his nose and mouth to see if you can get it started. This is what I did when my snake took a long time to shed. But then again mine wasn't injured. I hope things will be fine, my thoughts are with you.
Donna
Donna