GDM2 Setup is a GUI configuration tool for the new GDM (2) something that was missed by a lot of people. It doesn't have as many options as the old GDM setup tool, but that's because the new GDM2 doesn't support too many customizations.
Add the GDM2 Setup PPA in your source list using:
sudo add-apt-repository ppa:gdm2setup/gdm2setup
Update source list using:
sudo apt-get update
Install GDM2 Setup using:
sudo apt-get install python-gdm2setup