No Sale - I remember reading your story. I don't think of fantasizing in the same way it seems your wife is doing it.
I've generally only fantasized while trying to MB (I say trying because that isn't very successful these days either). It is always a faceless person - no one well known.
There was one exception where I knew my H was waiting up for me to have ML (we had talked about it earlier and I think I had offered or suggested - can't quite remember) and I was finishing a movie. I was not in the mood at all. So, when I went to bed and he started, I visualized the actor from the movie - who was not a well known actor.
I can try taking one of my fantasies and applying it while ML. But again, it is more of a faceless person and more about the setting and what is happening.