Custom window drop shadow without AllowsTransparency in wpf

Hi
I'm working on a program that will have a window with custom drop shadow (custom color and custom blur radius) like Visual Studio 2012 (Has Violet drop shadow and blur radius)

I have seen a lot of posts say set AllowsTransparency to true and create a border with the drop shadow you want to and change its Margin to fit the drop shadow inside the window but I won't to do it that way because I won't allows transparency because of performance issues and other issues and Maximize with border Margin issues.
Also I have seen a lot of posts say Use DWM (import DWM DLLs or use WPF window chrome) to make the drop shadow to the window but in this way you will apply the default drop shadow to your window (I don't know if I can customize it).
I Know that I can draw any where on my screen with MFC or GDI and native C++ but in this way it will be very hard to make the shadow and it will be software rendering not hardware which cost a lot of performance.

I wonder how did Microsoft create the Visual Studio 2012 GUI with WPF? and I want to know how to do something like it.

So can any one help me to do that drop shadow?

Thanks in advance.