I drop my jaw so my mouth is wide open and the skin from under my jawline is stretched and moved up towards the lower cheek. Then shave diagonaly downwards from under the ear to the chin. This works for me.
Thats just what I do. Works out so that the skin normally AT the jaw line is moved up a bit (or the jaw moved down) so I never actually shave where the jaw is at the time I am shaving. (To repeat what you said in different words.)