How to force Gnome's WM (metacity) to open a program window on a specific monitor?

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http://unix.stackexchange.com – I need to configure a dual-head machine using Debian 6 (and, hence, Gnome 2.30.2 and xrandr 1.3.3) so that it opens applications reliably on a certain screen. While it is trivial to move normal windows from one monitor to the other by just dragging their title bars, we need to run Stellarium, which opens an undecorated fullscreen window that doesn't even respond to ALT-dragging it. It also does not seem to use the standard X command line switches -geometry, -display and so on. Since this is a machine that will be shared by many users, I am especially interested in simple, intuitive and doc (HowTos)