You can register to the site without a last name, you cannot become a citizen without choosing a last name. And that is generally the easiest way to add a last name. When you get twenty-five posts and can apply for citizenship, you can add it to the info that you send in.
If you would like to...
Welcome, if you have any questions, or just want to chat, feel free to message me!
I have to admit, love your name because I'm another huge fan of the series!