如何处理添加到ObservableCollection类型的附加属性中的项

public class CustomObservableCollection<T> : ObservableCollection<T>
{
    public string AdditionalProperty { get; set; }
}

public class CustomCollectionWrapper<T>
{
    public ObservableCollection<T> Collection { get; set; }
    public string AdditionalProperty { get; set; }
}

public static class AttachedProperties
{
    public static readonly DependencyProperty AdditionalPropertyProperty =
        DependencyProperty.RegisterAttached("AdditionalProperty", typeof(string), typeof(AttachedProperties), new PropertyMetadata(null));

    public static string GetAdditionalProperty(DependencyObject obj)
    {
        return (string)obj.GetValue(AdditionalPropertyProperty);
    }

    public static void SetAdditionalProperty(DependencyObject obj, string value)
    {
        obj.SetValue(AdditionalPropertyProperty, value);
    }
}

<ListBox ItemsSource="{Binding MyCollection}">
    <ListBox.ItemTemplate>
        <DataTemplate>
            <StackPanel>
                <TextBlock Text="{Binding}" />
                <TextBlock Text="{Binding Path=(local:AttachedProperties.AdditionalProperty), RelativeSource={RelativeSource Mode=FindAncestor, AncestorType=ListBoxItem}}" />
            </StackPanel>
        </DataTemplate>
    </ListBox.ItemTemplate>
</ListBox>