DummyPanel.cs

  public class DummyPanel : Canvas
    {

        ContentControl control;
		VisualElement element;
        public DummyPanel(VisualElement element)
        {
			this.element = element;
	        DispatchAdd();
        }

        void AddControl()
        {
            if (control != null)
            {
                Children.Remove(control);
            }
			Width = 200;
			Height = 200;
            control = new ContentControl();
            control.Content = "UWPApplication";
			SetLeft (control, 200);
			SetTop (control, 200);
			Children.Add(control);
            control.InvalidateMeasure();
            control.InvalidateArrange();
			((IVisualElementController)this.element).NativeSizeChanged ();
        }

        internal IAsyncAction renderSeriesAction;

        void DispatchAdd()
        {
            if (renderSeriesAction == null)
                renderSeriesAction = Dispatcher.RunAsync(Windows.UI.Core.CoreDispatcherPriority.High, AddControl);
        }

    }

RendererExt.cs

[assembly: ExportRenderer(typeof(Xamarin.Forms.Label), typeof(App2.UWP.LabelRenderer))]
namespace App2.UWP
{
    public class LabelRenderer : ViewRenderer<Xamarin.Forms.Label, DummyPanel>
    {
        DummyPanel panel;
        protected override void OnElementChanged(ElementChangedEventArgs<Xamarin.Forms.Label> e)
        {
            base.OnElementChanged(e);

            panel = new DummyPanel (e.NewElement);

            SetNativeControl(panel);
        }
    }
}