Jumper/coat/other item of clothing between yoke and passenger if at all possible - the bolt holding the shoulder strap in the Cessnas I have flown don't look particularly substantial, so I would assume a sufficiently sudden stop might dislodge it. Crossing arms over chest seems like a good idea I will adopt.
The other thing I would advise is for the passenger to pull their feet backwards as hard as possible, as it rather looks like the legs would flail forwards in a sudden stop, potentially injuring them against the sharp edge of the bottom of the dashboard, which wouldn't be ideal if one wants to exit the aircraft under your own steam...
Harness as tight as poss, door unlatched and headset off on PIC's instruction at short final are also conducive to a better outcome, as is a calm head if at all poss...