Although such an idea is somewhat popular, but the problems of the Weimar Republic can not be solved simply by a living Rathenau or Stresemann.
Weimar had deeper problems that threatened democracy at the time:
The state administration, ie judges, administrators and the Reichswehr, was full of people who rejected democracy and wanted a right-wing dictatorship. Right-wing rebels were often punished very leniently, while left-wingers were also sentenced to death. The conservatives of the Weimar Republic had never accepted a liberal democracy, but longed for an authoritarian presidential dictatorship.
With the Great Depression, the time of stable governments was over. This was partly because the parties in the center and also the SPD had to suffer dramatic losses, while the anti-Weimar forces were gaining. This was mainly because the SPD, Center and DDP saw no alternative but an unconditional austerity policy known as deflationary. There were plans for investment and stimulus programs, e.g. from the unions, but the SPD did not dare to accept them because, firstly, they did not want to be doctors on the deathbed of capitalism, and second, because they saw no way to implement those plans.
The only parties that found a comprehensible answer to the crisis for most people was the KPD, especially for workers. And on the other side it was just the NSDAP, which could promise all people "work and bread" with Gregor Strasser's "immediate program" of 1932.
Quite apart from the fact that at the head of the Weimar Republic was a man who thought nothing of democracy and was willing to eliminate it at the first crisis phenomenon. As early as 1930, Weimar was no longer a functioning democracy, and von von Hindenburg was explicitly intent on doing so.
So I think that would you need a few PODs to save Weimar:
At first, prevent the win of von Hindenburg in 1925. Let's say the KPD follows orders from the Comintern and helps electing Wilhelm Marx in the second run-off.
Then, you would have to need a KPD that, while not supporting Weimar, doesn't destabilize it. Without the KPD supporting the referendum against the Young Plan it may doesn't become so dangerous to government.
At last, you would have to need democratic center-left governments who try to actively combat the depression. They need to give the economy a stimulus package and jobs to the workers or otherwise the NSDAP will still gain a lot of votes.