Screen names with Facebook and Google authentications

Is it possible to auto generate screen names with the provided Facebook and Google authentication systems? I've enabled the authentication but when signing in the first time it will ask you to enter a Screen Name with the authenticated email automatically filled in. Once completing the CAPTCHA the system feeds back and says "this email address is already used, would you like to login?" This happened with both Facebook and Google signup and sign in pages.

It would be great if the screen name is autogenerated using data from "first name" during authentication. So the user is just logged in without the need to enter more info.

I can take some screen grabs if this doesn't make sense.

Thanks everyone. I just started wrapping my head around the BLOX system last week and It's awesome. I look forward to learning more and hopefully upgrading to FLEX soon.