Is there a way of intercepting some method calls without making any code changes around the method itself?
I don\'t need to inject any custom behaviour at runtime,
You could take a look at Aspect Oriented Programming, and see if it's a solution for your situation.
For instance: http://docs.castleproject.org/Default.aspx?Page=Introduction-to-AOP-With-Castle&NS=Windsor&AspxAutoDetectCookieSupport=1
http://fgheysels.blogspot.be/2006/11/aspect-oriented-programming-in-net.html