You cannot get out of his contract. He is forcing you to either keep him on your ML roster, or release him.
If you release him, you are still responsible for next season's salary. In this case, he would not become a "true" free agent because he is still under contract. He just ends up in the FA pool, available to be signed by anybody for the ML minimum. However, if there is a team or mutual option for next season, then the 25% buyout is automatically invoked. You end up paying only a quarter of his salary, and he then become a true FA.