Flying . . .You want to set a trap that may result in the ruination of this husband's and wife's ( and kids if there are any) lives?
No, but if I have a friend who is exposing his wife to disease and doing it regularly, rather than telling her, and she needs to know, and having her lash out at me, I'd just figure out a way for her to catch him. Otherwise, she might not find out until she has contracted AIDS.
Do you think this man isn't already messing up her life and that of any kids involved? Men like this rarely go home and treat their wives and kids like they should be treated. In no way does this husband have the right to endanger his wife's health and even risk exposing her to a disease which could eventually take her life and deprive any children of their mother.
I've known too many people who exposed affairs or this type of behavior to friends and it backfired on them. Better to let the spouse discover this on their own. Visiting a prostitute regularly is not the same as an affair. This is much more dangerous and the innocent mate absolutely has every right to know.