Is it possible to force a monitor to stay in the server layout?

[Sven Berkvens-Matthijsse]

Hello,

I can't seem to find an answer to my question anywhere on the web.
Either my use case is weird, or I'm not searching correctly :-)

I have X.org server 1.11.3 running on Ubuntu. I'm using the radeon
driver with a Radeon HD6450. I have three monitors connected to the card
(all three monitors have a DVI input), and I've set up the server to
have all three monitors in one large desktop. This works brilliantly!

Sometimes, I need to connect one of the monitors to another PC or other
equipment with a HDMI or DVI output. My problem is that if I pull out
one of the cables that is connected to the HD6450, that the card (and
the X server) will detect that the monitor has been disconnected from
the card. Consequently, the desktop size is modified and all my Gnome
panels will be jumbled. If I reconnect the monitor, it comes back
online, but the positioning of the windows and panels is not restored to
what it used to be.

What I would like is to be able to tell the X server that I don't care
whether monitors are disconnected or not, and that it should keep the
desktop size fixed, no matter which monitors are connected. My X
configuration file includes a full server layout section, and also
contains the resolutions of the monitors. Therefor, it should be
possible, I guess, I just don't know how. Perhaps the current software
is not able to handle this specific situation. I can live with it if the
monitors need to be connected at the time that the X server starts. As
long as I can disconnect them later on without the server layout and
desktop size changing.

I realize that most people want the behavior that the X server exhibits
currently, because in their case it will probably be an external monitor
that is connected to a laptop on occasion. So I probably want something
odd :-)

Any help or pointers will be greatly appreciated. If the software is
currently not capable of what I've attempted to describe, I'd also like
to know, of course.

-- 
With kind regards,
Sven Berkvens-Matthijsse