New employee in skimpy attire: Can we create a dress code without singling her out?

Q. Our company is very casual and currently has no dress code in place. A recent hire is a young woman who is very well endowed and who wears very revealing attire--low cut tops and very short skirts. Our staff is predominantly male, and this has become not only a distraction, but a frequent topic of conversation amongst them. How can we implement a dress code now without appearing to be singling anyone out? – Jeanne, Florida