ugh,,so sorry to hear this crappy situation for you. Sorry, I don't have any success points about this situation.
However, do I understand she doesn't take your son to meetings? Not to use your son at all in this battle. However, try to throw positive energy into your son now. Use Sundays as family time. She should always feel welcome to come on your outings. Create for your son a positive life. What does he love? Always develop in him love for schooling, learning, the positives of this life now. Make your bond with him, with love, attention, and activities, activities, activities.
The WT world is so boring for a child. You can offer a world of positives, the WT world only teaches negatives, and a false dream world. Talk about things in life at his age level, teaching thinking ability for him. Express your 'unconditional love' to him, no matter what. He will never hear such talk in the JW world. Teach him to also love his mom and always to give respect to her.
He will learn so many good things from you. He will not forget. If you have that door open for him to feel like he's got a true choice, it is very most likely (99+% likely), he will be drawn to your real world. He will not be drawn to a world that DFs. He will have you to encourage college. In time, hopefully, he will have school friends and sports friends, or ones with similar interests.
Your wife has a right to believe as she will. Also, try to hope she will of her own re-evaluation see a more positive life than the one she grew up in, one that DFs, and see that is not the world she wants for her son.