gistfile1.cs

public static class HtmlDocumentExtensions
   {
      public static object ExecuteScript( this HtmlDocument document, string methodName, object[] args )
      {
         dynamic body = document.NativeElement;
         object script = body.document.script;

         return script.GetType().InvokeMember( methodName, System.Reflection.BindingFlags.InvokeMethod, null, script, args );
      }
   }