At race meets etc every one hooks their helmet to the bike, hundreds of them, not heard of any going missing yet, dont want to carry it around,
On my vfr there was a lock for this but not on the fzs1, so that lock you showed earlier up would go through the chin gaurd then lock anf place the lock under the seat,pillion possibly then lock the seat in position, the lock should be stuck under the seat,,should do the job.