Do you want both your names appear always or will there be times when you'd want your or his name only?
I'm asking because if both your names should appear all the time, you could register a 'common user' (this way both of you will keep your own personal user accounts, which you can use if you want to post something as your OWN opinion only), then after this user has been created, add it to your blog as an admin/editor/author/contributor... whatever roll you want it to have. Then login as this user, click on 'my profile' and on the left side, in the 'nickname' field, type both your name and his.
Just my two cents. Maybe someone else can come up with a better idea/solution?