Tightening ties between Opole and Racibórz duchies and Poland is easyily doable, although it does not mean instant incorporation, still, it makes it easier in the future. Duchy of Opole was already under control of Polish Vasas, and before it happened there was chance for exchange of Bari and Rossano and Duchy of Opole between Habsburgs and Jagiellons.
Good occassion to grab more of Silesia was during rule of George of Podebrady in Bohemia, although Jagiellons were too successful in that case-instead of Silesia they gained whole Bohemian crown. If George of Podebrady made no pact with Casimir IV then King of Poland would accept Pope's offert and would join anti-Hussite crusade.