ScaleX: 0.5 / ScaleY: 0.5 / RenderTransformOrigin: (0.25,0.25)

   
  
<Window x:Class="Workspace.DockExample"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="Workspace" Width="640" Height="480">
         <Canvas Width="250" Height="250">
           <Rectangle Height="50" Width="50" 
             Fill="#CCCCCCFF" Stroke="Blue" StrokeThickness="2"
             Canvas.Left="100" Canvas.Top="100"
             RenderTransformOrigin="0.25,0.25">
             <Rectangle.RenderTransform>
               <ScaleTransform ScaleX="2" ScaleY="2" />
             </Rectangle.RenderTransform>
           </Rectangle>
         </Canvas>

</Window>