Displaying modal dialogs using PRISM 4

I'm developing a .NET 4.0 application using PRISM and MVVM, as well as WPF.

I currently have a shell subdivided in regions, with views inserted in them. When the user clicks on a button in one of the views, I would like a custom-made modal dialog to be displayed on top of all the views, but still within the same shell.

I looked at the StockTrader RI example and their implementation of the RegionPopupBehavior. Basically, they created a dependency property which allows them to define regions with a specific, custom-made behavior. The behavior is the one in charge of handling it's associated view's rendering, hence displaying it as a popup window.

The only downside to this approach is that all the other views are still active, so the popup isn't modal. I guess this can be resolved by manually disabling all un-needed regions in the shell, but I'm not sure how "clean" this is.

I was wondering if there were a better and simpler approach to displaying modal pop-up views in Prism ?

You might be interested in a custom PopupUserControl I have posted on my blog that behaves like that.

Usually I use it like this:

<local:PopupPanel 
    Content="{Binding PopupContent}"
    local:PopupPanel.PopupParent="{Binding ElementName=SomeParentPanel}"
    local:PopupPanel.IsPopupVisible="{Binding IsPopupVisible}">

    <local:PopupPanel.Resources>
        <DataTemplate DataType="{x:Type local:SomeViewModel}">
            <local:SomeView />
        </DataTemplate>
        <DataTemplate DataType="{x:Type local:DifferentViewModel}">
            <local:DifferentView />
        </DataTemplate>
    </local:PopupPanel.Resources>

</local:PopupPanel>

Although you can also just write the Content in the popup instead of binding the Content property

<local:PopupPanel 
    local:PopupPanel.PopupParent="{Binding ElementName=SomeParentPanel}"
    local:PopupPanel.IsPopupVisible="{Binding IsPopupVisible}">

    <Border BorderBrush="Blue" BorderThickness="2">
        <local:MyUserControl />
    </Border>
</local:PopupPanel>