WP7 move listboxitem beyond item borders

Question

Hello,

I have a listbox with a custom itemtemplate (stackpanels). I try to animate the items so that they all move down from the top of the listbox. The problem is that when I modify the Y coordinate, it moves the listboxitem text only inside the item's boundaries, so I cannot simulate falling items down from the top.

    <DataTemplate x:Key="CustomListBoxItemTemplate">
    <StackPanel x:Name="item" Orientation="Horizontal" Margin="5, 5, 5, 5" Opacity="0" Loaded="item_Loaded">
            <StackPanel.RenderTransform>
                <TranslateTransform x:Name="translate" />
            </StackPanel.RenderTransform>
            <StackPanel.Resources>
            <Storyboard x:Name="item_Loaded" BeginTime="00:00:00">
                <DoubleAnimation From="0" To="0" Storyboard.TargetProperty="translate.Y" Duration="00:00:00.4"/>
                <DoubleAnimation From="0" To="1" Storyboard.TargetProperty="Opacity" Duration="00:00:00.4"/>
            </Storyboard>
        </StackPanel.Resources>
        <TextBlock Margin="15, 0, 0, 0" Text="{Binding}" FontSize="24" TextWrapping="NoWrap" />
    </StackPanel>
</DataTemplate>

Here is the code of the animation:

 private double starttime = 0.0;
    ...
    DropDownList = new ListBox();
    DropDownList.ItemTemplate = (DataTemplate)this.Resources["CustomListBoxItemTemplate"];
    ...
    private void item_Loaded(object sender, RoutedEventArgs e)
    {
        this.StartAnimationFromResource("item_Loaded", sender as FrameworkElement);
    }

    private void StartAnimationFromResource(string animationName, FrameworkElement element)
    {
        Storyboard sb = element.Resources[animationName] as Storyboard;
        sb.Stop();
        Storyboard.SetTarget(sb.Children[0], element.RenderTransform);
        (sb.Children[0] as DoubleAnimation).From = (starttime/0.05) * -30; //Canvas.GetTop(element);
        //(sb.Children[0] as DoubleAnimation).To = (starttime / 0.05) * 30; //Canvas.GetTop(element);
        Storyboard.SetTarget(sb.Children[1], element);
        sb.BeginTime = TimeSpan.FromSeconds(starttime);
        starttime += 0.05;
        sb.Begin();
    }