Hi lilbit,
It's always tough to get humans to change their ways...especially when they think they're right

A couple suggestions though:
1) Advising him that his behavior will make matters WORSE and lead to more problems with her down the line.
2) Seeking the help of a professional to help get the message accross. Even providing a book that speaks to the proper way to housebreak often helps (that way the info is not seen as coming just from you). My book (The Human Pack) has a section on proper housebreaking methods but there are many great books out there that should help.
Hope that helps

-Jenn
www.pandoraspetservices.com