Oh, this is almost too easy. It's almost diabolical. Many here have posted and reviewed the same book, with good results.
The trick is to make your wife NOT think you are tricking her into doing your fantasy, but to have fun and make this into a game for her and you.
There is a book called The Faithful Hotwife, and I found it on Amazon but some others said they found it in an adult book store also. It was written from a woman's perspective to explain to other women about men's lure to hotwifing, but it's also a great read as a couple. The fun part comes in where she leads the couple to take hotwife challenges that slowly build up into some pretty fun and daring challenges. It's all presented as a game so your wife will play along, which normalize the hotwife lifestyle in her mind. This isnt you telling her to do this or that, it's the book, which makes it OK, and takes the pressure off of you.
My wife really got into the challenges, and it was about a month into this when she removed her panties while we were sitting at table in a crowded restaurant bar, and passed them across the table to me in front of my brother. That was her challenge from the book and she did it. What a game changer.
Keep it fun, and you will be role playing the hot wife life in no time.