Post-1943 German Prussia is impossible IMO, but Pomerania and Silesia are pretty easy. Just have Truman push for an occupation zone up to the Elbe River, then Stalin retaliates with eastern 1925 borders for his occupation zone, bar East Prussia of course.
The only thing I can imaginer that would allow for a German Prussia is if an anti-Polish person got the influence of Stalin, who denied Poland even southern Prussia. But why the Russians would allow Germans to stay there I do not know, I can only imagine if, say, the war went on for longer and a more thorough Holocaust amongst Slavs began, as well as the war generally leading to more Soviet deaths, which may make Russian settlement of East Prussia impossible.
Thus, whilst Stalin annexes Prussia as an SSR, he is forced to keep the Germans there to maintain the area economically.
However the above Prussian scenario is near-ASB, if not total ASB...