You would have to get an attorney and go through the legal process of getting it changed.
My Husband Got A Girl Pregnant While We Were Separated. Her Boyfriend Signed The Birth Certificate And They Gave The Baby His Last Name. We Have A Paternity Test Showing My Husband Is The Father. How Do We Get The Birth Certificate Changed?
Don't think you can, but hey, next time tell him to stay friendly with his squeeze for a mere 9 months and he can be the proud pop(at least on paper).