I don't think anyone has mentioned this, but you have to mess with WW1 in big ways. Why? The Great Depression.
Just because you have a bad treaty of Versailles and everything that follows until 1929 doesn't make or break Hitler, it's the Depression that makes the Nazis.
I don't know for sure how you do all of this as you would have to have a totally different person for France at the conference and most likely England. Have the USA stay out (mainly, what I mean is they are pro British and France) William Jennings Bryant goes as a observer to the conference.
Maybe a Constitutional Monarchy in Russia and repudiation of the Treaty of B&L, on Germany's "own idea". The Germans for sure need a new Kaiser in a very Constitutional Monarchy (like GB today). I would allow a uniting of Austria and Germany to offset loss of land. I can see allowing the Sudatenland to stay German. Have the war over by 1917, with a TKO against the Central Powers.
Finally, give the Japanese something a lot better than what they did.
1 of these, multiple actions, all of them? You should last.