I have participated in the operations of a voting station in France, and the method you describe would be incredibly risky, unless all the voting station is in

I have participated in the operations of a voting station in France, and the method you describe would be incredibly risky, unless all the voting station is in (which you can not guarantee). Also even then, one group never opens more than a few hundred ballots, so the corruption would be limited to a couple ballots or become super obvious.