Let him be committed to Mar-A-Lago converted to a nursing home for reforming delusional Birthers. He spends so much time there anyway that he’ll believe the cover story that he has to stay there because the White House is being swept for the listening devices Obama left behind.
There he can spend his days ineffectually tweeting out his usual lies and bile. Various aides and orderlies can call him “Mr. President” and otherwise maintain his fantasy that he is still in charge. He can even have a fake briefcase that he’s told contains the “nuclear football.”
It seems the most humane thing to do.