Comment 1 for bug 880601

Here's a simple patch that implements the feature.

I edited LayoutPanel in the DesktopLayout module, and added another panel called "layoutProvidedPanel", exactly the same as the propertySheet.

Then:
1) If a panel is provided by the plugin from getSimplePanel, then it is put into the new layoutProvidedPanel. layoutPrivdedPanel is shown, and propertySheet is hidden.
2) If a panel isn't provided, then layoutProvidedPanel is cleared and hidden, and propertySheet is shown.

A plugin that manifests this ability is [some might say "suspiciously"] already working for this:
http://icculus.org/~chunky/stuff/gephi_graphviz/