Contacting a potential bull “out-of-the-blue”??

Regardless of what you say or how you say it, it’s going to be awkward coming from you. As you already know, the best approach is for her to contact him, but short of that, I would suggest arranging something so they can be physically together and be allowed some opportunity for flirtation. Evidence of her attraction to him, through her behavior, will make following steps in this direction a little more comfortable/natural.

Whatever you do I wouldn’t do it behind her back.

Well, any updates? Do let us know. As most posters have already said, it is much better coming from her. She could get flirty or even make an overt invitation so there is no time wasting. Once she has him on the hook, then she can introduce the situation to him. I find this works much better from personal experience.

Coming directly from you, a man he does not know could possibly freak him out. Saying that, i wish that would happen to me. All my experiences as a Bull have been initiated by the wife;  There is nothing sexier than a man approach you to fuck his wife!

There would be nothing wrong with the husband contacting the potential bull in this case.  The wife has already indicated a desire for the man as a sex partner so it could very well be in everyone’s interest to get the ball rolling, so to speak.  Since it would be an anonymous “cold call”, the husband could simply lay it out pretty much like he did here.  That way, from the very start, the subject of the communication would be right up front.  No innuendoes, no oblique references, no misunderstandings.  If the target shows an obvious interest, the collusion between husband bull could get much more personal very quickly and the wife could be brought into the conversation.  After that, it would be a matter of letting nature take it’s course.