This one is a little tricky.
The ShowDesktop is not directly accessible only the buttons itself via the Qt-DCOP bridge.
The Qt-DCOP bridge allows to call slots on Qt objects, in this case the button for showing the desktop.
[code:1]
dcop kicker $(dcop kicker qt objects | grep ShowDesktop | head -n 1 | sed "s#(# #g" | awk '{ print $1; }') toggle
[/code:1]
The part in $() transforms the object ID into a useable from for dcop.
dcop kicker qt objects
lists all qt objects of kicker
The grep filters the button. If one looks for a certain option, grepping for usualy names is the only way to find it (short of looking into the application source)
In this case I tried "desktop" and then "Desktop".
The commands after grep remove the unnecessary output, there might be better ways to do this
toggle is the actual action invoced on the button.
Cheers,
_