That is true, but getting them on the ballot is a state by state thing, and there would be many states where it would be too late.
We learned in 2000 (Gore vs. Bush) that "intent" is everything. Even a partially-punched chad indicated intent. In Dem-controlled states, looking for - and straining for - a Trump defeat - they will deem a vote for Biden will mean a vote for "X" placeholder who took his place.