It's not going to be easy to do it without outing you. He could be nonspecific, as in: "There have been incidents regarding certain employees' conduct around [your name], and I don't want it to happen again." Or: "Private details of [your name]'s personal life have been discussed in the workplace and this is unacceptable." Kind of a you-know-who-you-are type of thing. But this might provoke interest in you by employees who wouldn't have otherwise noticed you.
A better solution might be to ask your boss to meet privately with the employees who have committed these offenses. That way, they know their boss disapproves of their conduct, but you don't alert everyone that you're trans.
By the way, when you say you're not out, does that mean you're "stealth" or that you're not full-time yet?