I think more states are one way to tackle it. Another is to not give a sh*t as postwar period isn't really a thing in the scope of Vanilla.I'm not advocating for moving state borders so much as splitting up states so that there are more possibilities. AFAIK the post WW2 zones of occupation aren't possible to make accurately anyway in vanilla.
My preferred solution: enable peace conference province transfer between states, or add another layer of control called occupation zone or something, that allows for a per province Control of occupation.
Like basically a map draw tool, akin to battleplanner.