How do I get the PhysicalPath attribute of a VPP?  The VPP definitions are in episerver.config like this:

<add showInFileManager="true" virtualName="Documents" virtualPath="~/Documents/" bypassAccessCheck="false" maxVersions="5" name="SiteDocuments" type="EPiServer.Web.Hosting.VirtualPathVersioningProvider,EPiServer" physicalPath="C:\Sites\VPP\EPiServerSandbox2\Documents" />

I have the string "SiteDocuments" (the "name" from that config element), and I want to get the "physicalPath" (assuming it exists).  I've been up and down the API and can't figure out how to do this.