I had done some research previously on the matter after being contacted by Xavier Vanneste who blogged about this (http://blog.xvanneste.com/Lists/Billets/Post.aspx?ID=82), but was not able to figure it out at the time.
I’m currently writing sample code for my upcoming book on FS4SP and I had to figure this out. Time to bring out the tools!
One hour with the Visual Studio Reflector plugin and setting break-points internally in the SSA I finally figured it out. And in a way it was obvious.