P3P Header Info in MVC

I'm not sure where I'm suppose to put this in my Asp.net MVC website:

HttpContext.Current.Response.AppendHeader("P3P", "CP=\\\"IDC DSP COR ADM DEVi TAIi PSA PSD IVAi IVDi CONi HIS OUR IND CNT\\\"");

I put it in the:

public static void RegisterRoutes(RouteCollection routes)
{
  HttpContext.Current.Response.AppendHeader("P3P", "CP=\\\"IDC DSP COR ADM DEVi TAIi PSA PSD IVAi IVDi CONi HIS OUR IND CNT\\\"");
  routes.IgnoreRoute("{resource}.axd/{*pathInfo}");
  routes.MapRoute(
      "Default", // Route name
      "{controller}/{action}/{id}", // URL with parameters
      new { controller = "Account", action = "Logon", id = UrlParameter.Optional }
  );

}

But I get back

Response is not available in this context.

Anyone know where I am suppose to put this?