Adding RateMyApp for Windows Phone

Hi, I'm trying to add RateMyApp to a XF Windows Phone app (yes I will be looking at the Xam Components for iOS/Android later!).

RateMyApp is in Nuget (also see http://developer.nokia.com/community/wiki/Implement_"Rate_My_App"_in_under_60_seconds)

My main view is a TabbedPage and in the WP MainPage constuctor I have the usual

Content=MyApp.Shared.App.GetMainPage().ConvertPageToUIElement(this);

In order to use RateMyApp, I need to add the control in XAML as the last child in a grid so that when made visible it will cover the view. So I tried with this in the MainPage.xaml in the Windows Phone project

    <Grid x:Name="LayoutRoot" Background="Transparent">
            <Grid.RowDefinitions>
                <RowDefinition Height="Auto"/>
                <RowDefinition Height="*"/>
            </Grid.RowDefinitions>
            <StackPanel x:Name="stPanelMain" 
                        Grid.Row="0">
                <TextBlock Text="Demo" Style="{StaticResource PhoneTextNormalStyle}" Margin="12,0"/>
                <TextBlock  Text="Demo" Margin="9,-7,0,0" FontSize="40" />
            </StackPanel>
            <ctrl:FeedbackOverlay x:Name="FeedbackOverlay"
                                 Grid.RowSpan="2" 
                                 FeedbackTo="someon@somewhere.com"
                                 ApplicationName="MyApp"
                                 CompanyName="MyCompany"  
                               />
        </Grid>

and in the code behind I try to add my XF view

        public MainPage()
        {
            InitializeComponent();
            FeedbackOverlay.VisibilityChanged += FeedbackOverlay_VisibilityChanged;
            Forms.Init();
            var ctl = MyApp.Shared.App.GetMainPage().ConvertPageToUIElement(this);
            stPanelMain.Children.Add(ctl);
        }
        void FeedbackOverlay_VisibilityChanged(object sender, EventArgs e)
        {
            if (ApplicationBar != null)
            {
                ApplicationBar.IsVisible = (FeedbackOverlay.Visibility != Visibility.Visible);
            }
        }

I see my demo text blocks and the rating app pops up as expected, but when I remove the text blocks I don't see the tabbed page view at all.

I guess I can't put the main page content into a stackpanel/grid.

Any suggestions on how I should add RateMyApp, as I can't think how.

Thanks