Can FileVault show the login window as 'name and password', not 'list of users'?
I'm quoting this directly from a post in this thread at Apple Discussions:

This isn't a bug. This is the way FileVault-2's EFI boot authentication UI is built. When your Mac first starts up, EFI-boot takes over to decide what to do. It either continues to bring up the system to the typical OSX login screen, which is managed by OSX's system preferences, or it starts a special EFI pre-boot where it displays the FV2 unlock screen with the icons of designated OSX accounts approved to unlock the disk. Once you log on, the EFI unlock sequence carries forth your credentials, performing a single signon.
I have submitted a UI request (not as a bug) to be able to either edit the EFI boot screen (look at /usr/standalone/i386/EfiLoginUI directory, none are editable using normal applications) or ask that a feature is included, probably in the FV system preference pane, to add a custom banner.

For now, there doesn't appear to be a way to change it.