Extensions with .net 3.0

Hi Team,

How can we implement extensions in .net framework 3.0, I have tried below approach but they don't work,

namespace System.Runtime.CompilerServices
{
  [AttributeUsage(AttributeTargets.Method, AllowMultiple = false, Inherited = false)]
  public class ExtensionAttribute : Attribute
  {
  }
}
It says, to implement extension class should be static but if I declare class as static then error as 
static class should derive from objects.
Thanks,
Nikhil.