One problem is the Romanov family can not agree on who should be Czar. I think there would need to be a wave of monarchical restoration across Europe and a backlash against republicanism somehow. Maybe start in Hungary, have a general retreat of communism sooner under Gorbachev. Let former crown prince Otto freely travel to Hungary where he becomes very popular, and before the time of the fall of the Wall have Hungary adopt a constitutional monarchy, and offer Otto the crown of St Stephen? The former Tsar of Bulgaria was also active in politics and reasonably popular, so a restoration in Bulgaria next? Romania? Have the pre communist constitutions "restored" in these countries first.
Butterfly away the dictatorship in Greece and keep the monarchy there. Maybe a handwave and Italy doesn't become a republic post World War.