Let's face it. Most women and many men have "bi-sexual fantasies or dreams". This is normal. It does not make a person "gay/homosexual" to have these thoughts.
Now the trick as a Dominant woman is to know your mans bi-drive. Some males have a stronger bi-drive than others OR to a certain extent would consider acting on these desires under the guidance of a woman. For many men, moving the fantasy of say giving head to another man or having sex with them, as the submissive/bottom can become a reality with the presence of a woman. Both in terms of an act of humiliation in front of their Mistress/Wife/Girlfriend or the woman acts as a comfort shield so the man does not feel so "gay".
Such events can unlock more of a submissive's nature and take him to deeper depths in his submission through this kind of FemDom exploration and bisexual experimentation.
For woman who fantasize about seeing their man or perhaps sissy/crossdresser husband is to work this fantasy in conjunction with chastity. When men are horny and under the guidance of a Mistress anything is possible for a submissive with an open mind.