What you want to do is to make it his idea. It can be done I helped a German girl get her husband into it one time a few years ago. You have to gauge his interest level first, maybe the porn is good way or make up a story about a lady you know who maybe got caught by her husband and how they made up after. See what his reaction is. It doesn't matter what it is, we can work with it and nudge him in the direction.