WPF ComboBox Show Alternate Text - wpf

Question

I am trying to change the text of a WPF combobox button to something custom that isn't an actual selected item. The combobox control is setup with a custom datatemplate that allows it to contain checkboxes and what I'm trying to do is display "None Selected", [SelectedItem.Text] or "Multiple Selected" depending on whether zero items are checked, one is checked or more than one is checked. I found one solution on here that involved adding a new textblock instance that could display this text and then set the text of it to what I want to display. This works great until someone clicks and area next to the label of the checkbox and the text of that item shows up underneath my custom textblock causing weird overlap issues.
My assumption is a converter of some kind (which can replace the custom textblock as far as I'm concerned - no preference there), but I'm not entirely sure how to apply it. Here is my XAML thus far:
<Grid Grid.Row="4" Grid.Column="1">
<Grid.RowDefinitions>
<RowDefinition Height="Auto" />
<RowDefinition Height="Auto" />
</Grid.RowDefinitions>
<ComboBox x:Name="SubjectMatterList" Style="{StaticResource ComboBox}" ItemsSource="{Binding SubjectMatters}" Visibility="{Binding AdjunctListVisibility}">
<ComboBox.ItemTemplate>
<DataTemplate>
<StackPanel Orientation="Horizontal" MinWidth="125" MaxWidth="125" Margin="6">
<CheckBox Content="{Binding Name}">
<i:Interaction.Triggers>
<i:EventTrigger EventName="Checked">
<mvvm:EventToCommand Command="{Binding DataContext.SubjectMatterSelectedCommand, ElementName=GradeLevelList}" CommandParameter="{Binding}" />
</i:EventTrigger>
<i:EventTrigger EventName="Unchecked">
<mvvm:EventToCommand Command="{Binding DataContext.SubjectMatterDeselectedCommand, ElementName=GradeLevelList}" CommandParameter="{Binding}" />
</i:EventTrigger>
</i:Interaction.Triggers>
</CheckBox>
</StackPanel>
</DataTemplate>
</ComboBox.ItemTemplate>
</ComboBox>
<TextBlock IsHitTestVisible="False" x:Name="SelectedSubjectMatter" HorizontalAlignment="Left" VerticalAlignment="Top" Margin="10" Padding="10,6,0,6" Text="{Binding ComboBoxSubjectMatterText}" Visibility="{Binding AdjunctListVisibility}" />
<TextBlock Text="{Binding SelectedSubjectMatterText}" Grid.Row="1" Margin="10" Visibility="{Binding SubjectMatterSelectedVisibility}" />

Answer 1

http://blogs.microsoft.co.il/blogs/justguy/archive/2009/01/19/wpf-combobox-with-checkboxes-as-items-it-will-even-update-on-the-fly.aspx