There are lots of ways, none of them practical, especially with passengers on board.
Roughly, for each passenger there's an equivalent mass of fuel on the plane.
If you're working with thin margins that might not be enough, but if someone's shorted the craft half its fuel load, as was the case for AC143, I'd suspect this would be evident.
Other than a nerd-sniping exercise I don't see the point of going down this rabbit hole, because on an aircraft with pax the pilot's job isn't to screw around playing Chuck Yeager and estimate fuel with test pilot techniques.
If they can't fly with confidence that they're safe, then the pilot's job is to put the fucking aircraft on the ground as soon as able.