Silverlight 2.0 - scroll vertically, wrap horizontally

<UserControl x:Class="MyProject.MyControl"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:WinControls="clr-namespace:Microsoft.Windows.Controls;
      assembly=Microsoft.Windows.Controls"
    Width="400" Height="300">
    <WinControls:DockPanel LastChildFill="True">
    ...
<ScrollViewer x:Name="MessageScroll" HorizontalScrollBarVisibility="Hidden"
     VerticalScrollBarVisibility="Auto" BorderThickness="0" >
    <Controls:TextDisplay x:Name="TextDisplay"></Controls:TextDisplay>
</ScrollViewer>

<UserControl x:Class="MyProject.TextDisplay"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
        <TextBlock x:Name="TextDisplayText" TextWrapping="Wrap">
        </TextBlock>
</UserControl>