maybe next dev diary would tell us about fabricating claims and so
. On the other hand, I think there are several ways of achieving what you ask:
1- You invade and shatter the country. Keep which provinces you like (total exploitation or whatever kind of stuff is possible and you like) and liberate the rest (I am expecting to be able to choose provinces to keep when liberating).
2- Invade the provinces you want, then start bombing the country to stone age while destroying their convoys and doing other malicious stuff except taking more provinces. Thus, you can get the target country to sign a status quo peace. If I understood right, status quo peace is not white peace, but everybody keeping what they have on the moment of peace.
Or I am completely wrong and there is no way to do what you asked. There should be though.