You'd have to be very lucky to get away with it.
I was recently booked on a 3-cabin 772 ORD-NRT which was swapped to a Polaris retrofit at the last min, so I was in row 1 window.
Was chatting with some of the FAs pre-departure and overheard them say that the business cabin was fully booked even though several seats were empty very close to departure time. Some families came running up right before the door closed, but one of the middle seats in row 1 did remained open - app eventually updated to show that it was unoccupied.
I'm guessing that person misconnected, so some Y pax could have poached that seat, but you'd have to be very lucky and hope that the FAs don't double check.

TL;DR - Find the seat where a pax misconnected at the very last min on a full flight, AND hope they don't reassign someone to that seat AND hope that the FAs don't check their apps/manifest.