The fiction is that Joe was exposed to COVID (Jill or some staffer) and has to isolate.
The twist: Joe offers to debate via Zoom from his basement.
This way he gets to do "the honorable thing" by going through with the debate and earns sympathy points. At the same time, he can use teleprompter/earpiece without it being obvious.
Also, his handlers control the feed - they can have "technical difficulties" at any time if Joe hits a rough patch.
Still dangerous putting Joe on live camera, but maybe more manageable?
Biden might be like Yancey Pelosi and say Good Morning, Sunday Morning....