I created my own style of a menuitem for this. Not a beutiful solution.

<ControlTemplate x:Key="MenuPopupHeader" TargetType="{x:Type igRibbon:ToolMenuItem}">
   <Grid Margin="0">

    <Border x:Name="Bd" SnapsToDevicePixels="True" Background="{TemplateBinding Background}" BorderBrush="{TemplateBinding BorderBrush}" BorderThickness="{TemplateBinding BorderThickness}">
     <Grid >
      <Grid.ColumnDefinitions>
       <ColumnDefinition Width="*"/>
      </Grid.ColumnDefinitions>
      <Border x:Name="Caption" SnapsToDevicePixels="True" Background="#dde7ee" BorderBrush="#dde7ee" BorderThickness="0,0,0,1" CornerRadius="2,2,0,0" Padding="11,2,0,1">
       <ContentPresenter x:Name="Content" HorizontalAlignment="Stretch" Margin="0,0,7,0" VerticalAlignment="Center" SnapsToDevicePixels="{TemplateBinding SnapsToDevicePixels}" Content="{TemplateBinding Header}" ContentSource="Header" ContentStringFormat="{TemplateBinding HeaderStringFormat}" ContentTemplate="{TemplateBinding HeaderTemplate}" RecognizesAccessKey="True"/>
      </Border>
      <Border BorderBrush="#c5c5c5" BorderThickness="0,0,0,1"/> 
      
     </Grid>
    </Border>
   </Grid>
   <ControlTemplate.Triggers>
    <Trigger Property="IsEnabled" Value="true">
     <Setter Property="Foreground" Value="#00156e"/>
     <Setter Property="FontWeight" Value="bold"/>
    </Trigger>
   </ControlTemplate.Triggers> 
  </ControlTemplate>