To help things move toward your wife cuckolding you, you must build her sexual confidence up. This is done by encouraging her to wear sexier clothing and shoes when you take her out on the town.
"Don't take her out?" Then you need to start. Take her dancing, or just out to a bar. Let her go up to the bar and get drinks. Get her to interact with other men on her own, and get her used to the idea of other men being around her (without you around).
When she sees that other men are interested in her as a sex object, things will move in the right direction. She has to be comfortable with other men, and she isn't going to be able to do that unless you are taking her out to where she can find other men that she would be interested in.
Dancing is the most desirable of locations. She can dance with you there, and watch other men dance with other women. Eventually she can dance with other men. Once this starts, you can slowly fade out of the picture.
Drop her off and let her go in the club alone while you park the car (30 to 45 minutes is about how long you want her in the club without you). Take "important" phone calls outside so that you are not around and she has to dance with other men. Take long bathroom breaks, or arrange for her to have a girls night out with her friends.
The point is you have to make her get her sexual confidence back, and you have to get her used to the idea of being around other men without you. This builds her confidence up. This is what you want for her to accept the idea of fucking other men ... but you cant "frame it" that way.
It has to be presented to her as a way of enhancing the relationship (what she fears of losing most). If she can enhance one of the things she wants to hang onto, then she will be more accepting to try what you suggest.
Once she sees that there is no threat and that you are not operating with a hidden agenda, then she will warm up to the idea, but you have to let her "drive the bus".
Its a tough and tedious process. Nothing THIS good ever comes cheap, or easy so hang in there. For now, you all need to get her to feeling better about herself ... and get her exposed.
After that, things get a little easier.