Animated Expander Header Animation

Hi,

I just turn on the latest version, before this I used the version 2011.1.

I've made a new style to redesign my AnimatedExpander's header as follow

<Style x:Key="MyExpanderStyle" TargetType="{x:Type Controls:AnimatedExpander}">
    <Style.Resources>
        <LinearGradientBrush x:Key="{x:Static themes:AssetResourceKeys.ExpanderHeaderBackgroundNormalBrushKey}"
StartPoint="0,0" EndPoint="1,0" >
            <GradientStop Offset="0" Color="DarkBlue"/>
            <GradientStop Offset="1" Color="LightBlue"/>
        </LinearGradientBrush>
        <SolidColorBrush x:Key="{x:Static themes:AssetResourceKeys.ExpanderHeaderBackgroundHoverBrushKey}"
Color="DarkBlue"/>
    </Style.Resources>
</Style>

But now I want an animation on MouseEnter and MouseLeave event:

When the mouse enter upon the header, the color's header smoothly switch from my gradient (DarkBlue - LightBlue) to full DarkBlue and make the reverse operation on MouseLeave.

With my style above the change is direct, no animation.

On version 2011.1 I was able to use the property HeaderBackgroundNormal to perform my animation:

LinearGradientBrush currentBrush = uxExpander.HeaderBackgroundNormal as LinearGradientBrush;

if (currentBrush != null) {
    if (BindingOperations.IsDataBound(uxExpander, AnimatedExpander.HeaderBackgroundNormalProperty)) {
       uxExpander.HeaderBackgroundNormal = currentBrush.Clone();
    }
    PointAnimation a = new PointAnimation {
        From = currentBrush.StartPoint,
        To = new Point(0.999, 0),
        Duration = new Duration(TimeSpan.FromSeconds(0.2))
    };
uxExpander.HeaderBackgroundNormal.BeginAnimation(LinearGradientBrush.StartPointProperty, a);
}

 How can I perfom a similar animation on the last version? Without property on which apply my animation?

Thanks for you help

Kévin