Ammending my son's Birth Cert in California

my son wants to add my married name to the end of his legal name, to hypenate it (not delete legal name). he has used it since kindergarten is now in high school. everyone knows him by my last name. wants to have both names on birth cert before getting license. legal father still sends support, but hasn't wanted reg. visits for past 4 years has not even seen him in that time. only calls every 3 or 4 months for a short chat. how can i do this without legal fathers consent? step dad has raised him since age 2, son is 15.

[stacyg2]

I'm in MA and I had my son's name hypenated but I did have to get the birth father to sign the court papers. I don't know the laws in CA but in MA you need both parents to sign for a name change.