Changing the Application Path in IIS Developer Express

Question

Is it possible to run IIS Express (Beta from WebMatrix) with a path other than /?

There's no documentation so I've copied the default "applicationHost.config" and made the following change to the application path and virtual directory:

<site name="WebSite1" id="1" serverAutoStart="true">
  <application path="/x">
    <virtualDirectory path="/x" physicalPath="%IIS_SITES_HOME%\WebSite1" />
  </application>
...

When I go to http://localhost/x I get the error:

The requested page cannot be accessed because the related configuration data for the page is invalid.

What do I need to change to get this working?