How can I "Click Through" a control in WPF? - wpf

Question

I have an order entry form that has a ListBox with a list of line items. I have my items template, and one of the values is a ComboBox in each of my Items.
Now, my form can also create Credit memo's in addition to purchase orders, but when I am creating a credit memo, I want to put the words "Credit Memo" over the list box, however, the TextBlock covers the ComboBox in two of my line items. I would like to pass my click event through the TextBlock to the ComboBoxes but I'm not sure how to do it.
This is what I have, ( Maybe I am coming at this totally wrong, I am kinda a noob with WPF )
<ListBox SelectionMode="Single" Grid.Row="2"
ItemsSource="{Binding Path=LineItems}" HorizontalContentAlignment="Stretch"
IsSynchronizedWithCurrentItem="True" Background="#66FFFFFF">
<ListBox.ItemContainerStyle>
<Style TargetType="{x:Type ListBoxItem}">
<Setter Property="Background" Value="WhiteSmoke"/>
<Setter Property="BorderThickness" Value="1" />
<Style.Triggers>
<DataTrigger Binding="{Binding Path=IsPartBackOrder}" Value="True">
<Setter Property="Background" Value="Orange" />
</DataTrigger>
</Style.Triggers>
</Style>
</ListBox.ItemContainerStyle>
<ListBox.ItemTemplate>
<DataTemplate DataType="{x:Type Entities:SalesOrderLineItem}" >
<OrderEntry:SalesOrderLineItemCreate DataContext="{Binding}" DeleteSalesOrderLineItem="DeleteSalesOrderLineItem" Margin="0,3,3,0" >
<OrderEntry:SalesOrderLineItemCreate.Resources>
<Style TargetType="{x:Type OrderEntry:SalesOrderLineItemCreate}">
<Style.Triggers>
<DataTrigger
Binding="{Binding RelativeSource=
{
RelativeSource
Mode=FindAncestor,
AncestorType={x:Type ListBoxItem}
},
Path=IsSelected
}" Value="True">
<Setter Property="Background" Value="LightBlue" />
<Setter Property="Foreground" Value="Black" />
</DataTrigger>
</Style.Triggers>
</Style>
</OrderEntry:SalesOrderLineItemCreate.Resources>
</OrderEntry:SalesOrderLineItemCreate>
</DataTemplate>
</ListBox.ItemTemplate>
</ListBox>
<TextBlock Grid.Row="2"
Text="Credit Memo"
HorizontalAlignment="Center"
VerticalAlignment="Center"
FontSize="48" Height="Auto"
FontStyle="Italic"
Foreground="Red"
Opacity=".25">
<TextBlock.Style>
<Style TargetType="{x:Type TextBlock}">
<Style.Triggers>
<DataTrigger Binding="{Binding Path=OrderType}" Value="CR">
<Setter Property="Visibility" Value="Visible" />
</DataTrigger>
<DataTrigger Binding="{Binding Path=OrderType}" Value="CU">
<Setter Property="Visibility" Value="Hidden" />
</DataTrigger>
</Style.Triggers>
</Style>
</TextBlock.Style>
</TextBlock>

Answer 1

<TextBlock IsHitTestVisible="False" .../>