I had the same problem with how to handle the conversation when my H brought up the D subject. I had a phone session with a coach and he advised me to NOT do anything to help with the D process. You are right, if he brings up the subject, there is nothing you can do. I would agree with him, but tell him that you will wait for the papers from him, since you are too busy and have other things to do. If he really wants it, he can start the process and you will not stop him, but you will do what is best for you.
When my H came to the house for a second time (yesterday) to discuss D, I told him to go ahead and fill in the paper work and send it to me, and I would pass it onto my lawyer. He was surprised that I wanted to use a lawyer, since he wants to do it amicably, just like your H. You can read the whole update on my thread.
M:50 H:52 S28 (my S from previous marriage) M:17 + 3 BD: 06/12 S: 06/12 - H works in another state
