It's currently impossible to select "Not listed?" option in gdm login screen with just the keyboard - it'd be very nice if it were possible.

Also, it should ideally be the option "selected" by default when no other login options are available. This happens to be the case for me after upgrading from F14 - Fedora changed the starting uid for user accounts to 1000 from 500 in F14 and I didn't want to change anything on my user partition so I just changed the uid of my login account instead and am now left with an empty gdm login prompt that I can't use without a mouse.