How can the 1990s/early-2000s produce a Poland that seriously pushes for the restoration of its 1939 eastern border? Perhaps even to the point of occupying the majority-Polish parts of Belarus or Lithuania? Or even Zaolzie?
Is there any window-of-opportunity (or, to paraphrase Pilsudski, "door" of opportunity) in the 1990s where Poland can push for this and get the international community's blessing?
EDIT: Bonus points if this combines with other former-Warsaw-Pact revanchism, like Romanian claims to Bessarabia, or Hungarian demands to revise Trianon, to produce a new "war of the pygmies."