If he agreed with anything he read, he would likely bring it up. He's probably keeping his mouth shut because he's afraid if he talks to you much more about it, his conscience will eat him up and it will be the end of your friendship. Of course, it could be that he hasn't gotten around to reading it.
When I first got my hands on Crisis of Conscience, I was slightly afraid my eyes would melt out of my head while reading it.
After I "cracked the seal" and started sharing some information with my best friend, he couldn't keep his mouth shut about it. We talk about these things regularly. The first conversation we had was in the car out in front of his house. Afterward, he said to me: "Well, I'm going to go inside and get my sign ready for the District Convention."
I never initiate the conversation about JW matters though, because I don't want him to think he is being pushed by me to believe any particular thing. I think you are smart for leaving it alone. If he is interested in exploring, he'll read it and ask you questions. If not, hopefully he's good enough of a friend to allow your opinions and let you continue to fly under the radar.