WebBrowser c#: Как изменить UserAgent

Изменение UserAgent в WebBrowser

        [System.Runtime.InteropServices.DllImport("urlmon.dll", CharSet = System.Runtime.InteropServices.CharSet.Ansi)]
        private static extern int UrlMkSetSessionOption(
            int dwOption, string pBuffer, int dwBufferLength, int dwReserved);

        const int URLMON_OPTION_USERAGENT = 0x10000001;
        const int URLMON_OPTION_USERAGENT_REFRESH = 0x10000002;

        public void ChangeUserAgent()
        {
           string ua = "Googlebot/2.1 (+http://www.google.com/bot.html)";

            UrlMkSetSessionOption(URLMON_OPTION_USERAGENT_REFRESH, null, 0, 0);
            UrlMkSetSessionOption(URLMON_OPTION_USERAGENT, ua, ua.Length, 0);
        }