dual monitors - one desktop image spanning both?

[Wolfgang S. Rupprecht]

Is it possible to get one backdrop image in F16 to span both monitors in
a dual-monitor setup?  I'm using xfce4 and the desktop settings tool
seems to only offer a per-monitor image selection.  Is there some way of
selecting one image perhaps from gconfig directly?  Ditto for the login
screen.  Having the same cloned Verne image on both monitors is kind of
lame.  It would look a lot nicer if one image spanned both monitors.

-wolfgang
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