Creating directories during a copy using IFileOperation

Using Stephen Toub's IFileOperation wrapper for C# (link), which has been working well until now. Now I am trying to do a copy to gather files from network locations, each network location into its own subdirectory.

\\FOO\data into C:\gather\Foo_data
\\BAR\manage\current into C:\gather\bar\manage

And so on. The problem is in FileOperation.CopyItem. It must be because the destination directory doesn't exist yet—IFileOperation will create it during the copy, right? I used the technique from another question and changed Toub's FileOperation.CreateShellItem to this:

private static ComReleaser<IShellItem> CreateShellItem( string path )
{
    try
    {
        return new ComReleaser<IShellItem>( (IShellItem)SHCreateItemFromParsingName( path, null, ref _shellItemGuid ) );
    }
    catch ( FileNotFoundException )
    {
        IntPtr pidl = SHSimpleIDListFromPath( path );
        IShellItem isi = (IShellItem)SHCreateItemFromIDList( pidl, ref _shellItemGuid );
        Marshal.FreeCoTaskMem( pidl );
        System.Diagnostics.Debug.WriteLine( "Shell item: " + isi.GetDisplayName( SIGDN.DesktopAbsoluteParsing ) );
        return new ComReleaser<IShellItem>( isi );
    }
}

I stuck the Debug.WriteLine in there to check that it's working, and it seems to be working fine; it writes the path back out.

But IFileOperation.CopyItem throws an ArgumentException, and I can't figure out why. Am I not doing the "IShellItem for a nonexistent file" correctly? I suspect I need to get SFGAO_FOLDER in there, since I am trying to create an IShellItem for a nonexistent directory, not file, but how?