Modern UI Metro Chart - Thousand Separator

I'm generating some graphics using Modern UI Metro Chart , but in one of the charts the number would need to be shown with separator of thousands.

Searching I found this discussion: Add thousand separator and tried to make the change but to no avail.

I tried the change below:

<Style x:Key="NumberStyle" TargetType="TextBlock" >
    <Setter Property="TextAlignment" Value="Center" />
    <Setter Property="FontWeight" Value="Bold" />
    <Setter Property="Margin" Value="2 0 2 0" />
    <Setter Property="Opacity" Value="0.75" />
    <Setter Property="Text" Value="{Binding StringFormat=N}" />
</Style>