Comment 7 for bug 519372

I've tried it and it does work in principle. I did

gconftool-2 -s /desktop/gnome/peripherals/keyboard/general/disable_indicator -t bool true

then logged out and back in and the layout indicator was gone.

However there is no schema for the key, it has to be created manually and cannot be discovered by searching initially. Furthermore apparently g-s-d doesn't listen to the gconf notification, so there is no immediate effect when toggling the key. It seems to require a log-out/restart.