I figured out how to get it to work. I set the entire window to have the aero glass effect on it using the native API's and then a create a LinearGradientBrush for my background of the window. In the brush I used the Alpha properties of the brush and set the stops to have the top of the window go from white/opaque to white/transparent all very close to the top of the window.
<Grid>
<Grid.Background>
<LinearGradientBrush StartPoint="1,0">
<!-- This gradient stop is Fully transparent. -->
<GradientStop Color="#00FFFFFF" Offset="0.0" />
<!-- This gradient stop is fully opaque. -->
<GradientStop Color="#FFFFFFFF" Offset="0.1" />
</LinearGradientBrush>
</Grid.Background>
</Grid>
I 1 up'd Mikko Rantanen's answer because I used the article to add the glass effect I didn't have the code handy and it was a good simple article.