This is the best game I've managed to get. I did do this on easy mode, though
Viewing post in Social Democracy: An Alternate History comments
Improve relations with the KPD, always campaign with the unemployed so that your support doesn't suffer too much when the stock market crashes, consolidate support among the left and labor factions so that you can adopt the left plan normally and use Wotinsky(I butchered that name probably) to adopt the WTB-plan. Enact both ASAP. Get Braun elected by using good relations with the KPD and resources on the center. I chose Bruning as the emergency chancellor to reduce the chance of a march on Berlin. After that, it should be smooth sailing as you have all cabinet positions and a no-confidence vote can't really unseat you. Also, invest in Radio a lot.