Scale element in one direction

Hey guys,

I am adding an rectangle to my layout (below another rectangle) and I am a using a scaling adding animation.

<Scaling ux:Name="NewExScaling" Y="1" />														    
     <Change NewExScaling.Y="0.5" Duration="0.5" />														    

However, the animation looks goofy as the element is expanding from the top and bottom at the same time.

Is there any way to expand the element only from the bottom side, opposed to having it expand from both sides ?