it's not that it "promotes fouling accuracy" so much as to achieve accuracy, you need to be consistent.
the most consistent you could probably get would probably be to clean to bare steel between each shot. that way the barrel is always the same. after a shot, there's some fouling in the barrel that changes the friction, which affects the velocity and pressure. after the second shot, there's a little more.
since cleaning every shot is highly impractical, the next best thing is to shoot with a consistent coat of fouling on the barrel. while copper tends to adhere to itself and build up inconsistently, powder somehow, magically, seems to be self regulating, as it hits some point and just stays there.
in my experience, you need 5-10 rounds to foul it in, but after that, it seems to be consistent.
i don't know if you could apply oil in a consistent way, but if you could, i suppose that would work too. you'd have to test it.