Trump should announce he's changed his mind and will attend the inauguration and offer to help Joe with his lines / the oath if dementia acts up. Say it's a gesture of healing. If Joe disinvites him say he's fine sitting with America's hero citizen-soldiers rather than politicians and giving autographs and hats. He can get up and leave with his secret service detail after joe is sworn in. Trump pulls all the oxygen out of the room with his presence. He can even shout encouragement, "like you can do it Joe" and "come on man" if Joe stumbles. Ideally, he gives an interview as joe is giving his inaugural speech calling Joe a Pedo, but hoping he's mended his ways and been cured and the country will do ok under his leadership.