So don't draw a line? Use the point of the rule which is "does this person gain an unfair advantage"? We can have common sense laws if we want, there's no need for this sort of precision when the whole point is to determine an advantage.
I mean if we want to get REALLY technical, what does "played the ball" even mean? The moment the ball starts travelling in a different direction? When it has left the foot entirely? There's no such thing as "touching" on an atomic level. You don't touch the chair when you sit on it, the atoms from your body meet a point of equilibrium of forces with the atoms in the chair. "Clear air" between the ball and the foot? So they have to judge clear air anyway so judge clear air on the offside rather than the ball played
The problem with the precision argument is that if you're going to use it then you need to be as precise as possible. You can't be "a bit precise" because then logically the whole thing falls apart. Like many thing, you can either be as precise as possible or accept that precision isn't the goal and instead enabling the game to be fairer is.