Adding Connecting Lines to Prevent Pie Overlapping

You can add connecting lines with the PlotElement.LabelLine Attached property like the following XAML code:

<c1:DataSeries.PointLabelTemplate>

  <DataTemplate>

    <Border BorderBrush="DarkGray" BorderThickness="1" Background="LightGray"

            c1:PlotElement.LabelAlignment="Auto"

            c1:PlotElement.LabelOffset="30,0">

      <TextBlock Text="{Binding Value, StringFormat=0}" />

      <c1:PlotElement.LabelLine>

        <Line Stroke="LightGray" StrokeThickness="2" />

      </c1:PlotElement.LabelLine>

    </Border>

  </DataTemplate>

</c1:DataSeries.PointLabelTemplate>