It can be done at the county level and then you just send in the bogus numbers to the state level and the state level is D so they’re fine just going along with them.
I would think anybody on a county election board would be too worried about jail time to do that. How many counties per state needed to join in the fraud? Two or three? That would suggest 10 to 20 counties nationwide are complicit. Sounds like too many potential sources of revelation of the whole scheme. They had to keep the number of people in-the-know to a bare minimum.
Furthermore, it requires an order at the state level to stop counting. How was that planned and coordinated? Who gave the order?