How can I add “X-Content-Type-Options: nosniff” to all the response headers

As long as you’re using IIS 7 or above, it’s as simple as adding it to your web.config.

<configuration>
   <system.webServer>
      <httpProtocol>
         <customHeaders>
            <add name="X-Content-Type-Options" value="nosniff" />
         </customHeaders>
      </httpProtocol>
   </system.webServer>
</configuration>

Or you can add them using the IIS Management GUI, or even command line. Take a look at http://www.iis.net/configreference/system.webserver/httpprotocol/customheaders