You tell him "Do what feels honest for you, and share what's on your heart; I will neither ENcourage you nor DIScourage you," and then let him be. Don't prod him, don't put any words in his mouth or use him as a go-between to what YOU feel like saying to your husband. TRULY be neutral (don't "hint", for example, even while you're saying these politically-correct words that you'd really LOVE it if he did!), and then leave him be.
He will do what he will do. This is what I did with my adult daughters, and each confronted their mother in their own, and very different, ways, and on their own time.
