You can simplify this by taking the tension out of your shoulders at address, and keeping it out on the BS.
Is it simple if it doesn't work? I suspect he has tried not to do it, he knows he shouldn't. If the movement is habitualized and he isn't AWARE of the proper movement he will never change. My suggestion eliminates the shrug and replaces it with the proper movement. Albeit forced open, the door is no longer jammed and he can then learn to swing it freely.
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