User Defined Usernames with Ultimate Facebook?

Hi, just a quick question.

just wondering if it's possible to allow new users to create their own usernames when signing up with ultimate facebook?

i can see why user names would be insignificant in most use cases seeing as users would log in with facebook, however i'm thinking as usernames are a unique identifier in wp there may be an instance where i may use them to implement some social features further down the line.

cheers