Quoting "W. Martin Borgert" <debacle@debian.org>:
Also, I was under the impression that I don't need to set them anyway, when running Gnome (gnome-shell).
Interestingly, when trying on another machine (wheezy with Xfce4 instead of Gnome3) with the variables set, libreoffice talks to me. So it must be a configuration issue or missing package. If nothing helps, I can ask the user to switch from Gnome to Xfce. Cheers