I don't know if Congress can censure a president or not.
But I would have the House pass a motion of censure or a resolution condemning Trump's anti-democracy disputation of the election. Make the GOPers congressfolk go on record voting for or against the Are You On the Side of Democracy or Trump? resolution.
Try to get the same voted upon in the Senate. Mitch will no doubt block it, but try to pressure GOPs senators to go on record. Maybe Romney and few other GOP senators will go along. It'd be in the moderate GOPers interest to make the extreme Trumpeters look bad.
Try to force the GOP officials to condemn Trump's behavior and unfounded accusation of fraud and undermining of democracy, or have them vote pro Trump.