Currently the keyboard layout chooser in the top bar of unity-greeter (precise beta 1) shows the default system keyboard layout and/or the keyboard layout of already-logged-on users. The list is missing an "add keyboard layout" option.
I have LDAP-based users and I am deploying the same Ubuntu image to all the machines. Users are from multiple countries, so they use multiple keyboard layouts. I provide a default, but this is not ok for some instances. Because the user has never logged on before, he can't choose his keyboard layout, because it's not there. This is a chicken-and-egg problem.
Therefore, a feature to add an arbitrary keyboard layout to the list while on the logon screen is essential. This is already in GDM.
Alternatively, I would need to provide a subset of keyboard layouts for the countries I will deploy Ubuntu in, but as far as I know the default list only contains the single system default layout.
I am in a very similar situation. I have user information stored in LDAP and a default Ubuntu configuration managed by puppet. I would like to add multiple keyboard layouts to the drop-down menu in the unity greeter, but can't find a way to do this on a system level.