[CentOS] Remove/deactivate the session and language buttons in login screen

Hi All,

I'm using centOS 6.4 with openbox as windows manager. I modified
/etc/X11/xinit/Xsession file in orden to set up openbox as default
windows manager for all users (I changed gnome-session to openbox-session).
Now, I would like to remove or deactivate the the session and language
button in login screen. I tried to find these using gconf-editor but
without any luck. I could change the banner text message and disabled
user list but nothing for the other buttons.
Any clue how can I accomplish this?

Thanks in advance!