Using a different DataTemple when a WPF ComboBox is expanded

<ResourceDictionary xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">

    <!--Address DataTemplates-->
    <DataTemplate x:Key="AddressComboCollapsed" >
        <StackPanel Width="150" HorizontalAlignment="Stretch" >
            <DockPanel HorizontalAlignment="Stretch">
                <TextBlock Text="{Binding Path=AddressName}" 
                           DockPanel.Dock="Left" 
                />
                <TextBlock Text="{Binding Path=AddressType}" 
                           DockPanel.Dock="Right"
                           HorizontalAlignment="Right"
                />
            </DockPanel>
        </StackPanel>
    </DataTemplate>

    <DataTemplate x:Key="AddressComboExpanded" >
        <GroupBox BorderThickness = "1"
                  Margin = "0,0,0,3"
                  Width = "Auto "
                  HorizontalAlignment = "Stretch"
                  Header = "{Binding Path=AddressType}">
            <StackPanel Margin="3" 
                        HorizontalAlignment="Stretch"
                        MinWidth="250">
                    <TextBlock Text = "{Binding Path=AddressName}"/>

                <TextBlock Text = "{Binding Path=AddressLine1}"
                           Name = "tbAddr1"
                />
                <TextBlock Text = "{Binding Path=AddressLine2}"
                           Name = "tbAddr2"
                />

                <!-- City, State, and ZIP display -->
                <StackPanel Orientation = "Horizontal">
                    <TextBlock Text = "{Binding Path=City}" />
                    <TextBlock Text="," Padding="0,0,5,0"/> <!-- Put a comma between city and state -->
                    <TextBlock Text = "{Binding Path=State}" Padding="0,0,5,0" />
                    <TextBlock Text = "{Binding Path=PostalCode}" />
                </StackPanel>
            </StackPanel>
        </GroupBox>

        <DataTemplate.Triggers>
            <!--If the "AddressLine2" portion of the address is blank, then
				HIDE it (no need to display an extra blank line)
                
                This only works is AddressLine2 = "", not if it's null
            -->
            <DataTrigger Binding = "{Binding Path=AddressLine2}" Value = "">
                <Setter TargetName = "tbAddr2" 
					    Property = "Visibility" 
                        Value = "Collapsed"
                />
            </DataTrigger>
        </DataTemplate.Triggers>
    </DataTemplate>
    <!--End Address DataTemplates-->
</ResourceDictionary>