I push the skin on the side of my face up and backwards starting at a point roughly below the outside of my eye and level with the top of my earlobe. I then push my jaw towards the oposite side of my face using my jaw muscle, then i generally shave diagonally downwards from the corner of my mouth.
I also use my lip muscles to help with the stretch at different points.
I sometimes will move my chin subtley during the pass to alter its relative angle too.