Tengo una plantilla personalizada para un expansor que está cerca del código a continuación. Tuve que cambiar parte del código para sacar clases personalizadas, pinceles, etc.

<Style TargetType="{x:Type Expander}">
  <Setter Property="HorizontalContentAlignment"
          Value="Stretch" />
  <Setter Property="VerticalContentAlignment"
          Value="Top" />
  <Setter Property="BorderBrush"
          Value="Transparent" />
  <Setter Property="FontFamily"
          Value="Tahoma" />
  <Setter Property="FontSize"
          Value="12" />
  <Setter Property="Foreground"
          Value="Black" />
  <Setter Property="BorderThickness"
          Value="1" />
  <Setter Property="Margin"
          Value="2,0,0,0" />
  <Setter Property="Template">
    <Setter.Value>
      <ControlTemplate TargetType="{x:Type Expander}">
        <Border x:Name="Border"
                SnapsToDevicePixels="true"
                Background="White"
                BorderBrush="{TemplateBinding BorderBrush}"
                BorderThickness="{TemplateBinding BorderThickness}"
                Margin="0,0,0,10"
                Padding="0"
                CornerRadius="8">
          <DockPanel>
            <Border x:Name="HeaderSite"
                    Background="Blue"
                    CornerRadius="8"
                    Height="32"
                    DockPanel.Dock="Top">
              <DockPanel>
                <ToggleButton Foreground="White"
                              HorizontalContentAlignment="{TemplateBinding HorizontalContentAlignment}"
                              VerticalContentAlignment="{TemplateBinding VerticalContentAlignment}"
                              Margin="0"
                              MinHeight="0"
                              MinWidth="0"
                              Padding="6,2,6,2"
                              IsChecked="{Binding Path=IsExpanded, Mode=TwoWay, RelativeSource={RelativeSource TemplatedParent}}"
                              DockPanel.Dock="Left">
                </ToggleButton>                

                <ContentPresenter SnapsToDevicePixels="True"
                                  HorizontalAlignment="Left"
                                  Margin="4,0,0,0"
                                  ContentSource="Header"
                                  VerticalAlignment="Center"
                                  RecognizesAccessKey="True" />
              </DockPanel>
            </Border>
            <Border x:Name="InnerBorder"
                    Margin="0" >
              <ContentPresenter Focusable="false"
                                Visibility="Collapsed"
                                HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}"
                                Margin="{TemplateBinding Padding}"
                                x:Name="ExpandSite"
                                VerticalAlignment="{TemplateBinding VerticalContentAlignment}"
                                DockPanel.Dock="Bottom" />
            </Border>
          </DockPanel>
        </Border>
        <ControlTemplate.Triggers>
          <Trigger Property="IsExpanded"
                   Value="true">
            <Setter Property="Margin"
                    TargetName="InnerBorder"
                    Value="5" />           
            <Setter Property="Visibility"
                    TargetName="ExpandSite"
                    Value="Visible" />
          </Trigger>
          <Trigger Property="IsEnabled"
                   Value="false">
            <Setter Property="Foreground"
                    Value="{DynamicResource {x:Static SystemColors.GrayTextBrushKey}}" />
          </Trigger>         
        </ControlTemplate.Triggers>
      </ControlTemplate>
    </Setter.Value>
  </Setter>
</Style>

Como puede ver, hay dos ContentPresenters. Me gustaría que el primero usara Tahoma Bold como fuente en lugar del Tahoma predeterminado. ¿Cómo puedo hacer esto?