I was in a similar situation with my son who always wanted mine and my husbands and childrens last name.
His birth father has never been in the picture and never paid a dime to him. So for his 14th birthday, my husband and I went to an attorney to draw up a statutory declaration. However, he just did a deed poll name change. I did have to sign papers stating something to the effect that I was the sole parent in charge, something like that.
I can laugh now but I was in tears when he opened up the certificate and we also had silver dog tags engraved with his new name and a special note just for him.
We used it to open a bank account, change his school and employment records, and we took it to the US Embassy to get his new passport. The guy at the desk said they may not accept it but they did. He did say it had to be a statutory declaration in order to change it. This was done Jan 2009. The attorney did say that if it wasn't accepted he would do the statutory dec for us though.
It's been so nice having him with the same name. I know it's just a name but his siblings had our name.
We originally inquired about my husband adopting my son in the states but they made it sound like a long drawn out costly road. I got the feeling they couldn't be bothered so we left it at that.
Sorry that was so long winded.