My last mount that I had done was a pedestal mount and I got a cedar tree that had blown over and ripped it from the ground. I took my chainsaw and cut a hole in the back side of the stump and then bored a hole on the top. Worked great but the roots have to be cut back and that's tricky. My idea for your shoulder mount would be you could bolt a metal rod onto the back of your mount and then fashion some kind of pedestal to set it on. Good luck and post some pics once your done. I would like to see it.