How to add method in Sealed class

In Object Oriented world Sealed class is class which can not inherited, its sealed not more implementation get added. This was correct before C#3.0 invented. C#3.0 Comes with lots of new functionality like Extension Methods, Anonymous Types, Partial Methods, Automatic Properties and Object-Collection Initialization. Also there is major portion added to C# 3.0 which is LINQ, you can find