ASP.NET WebService, I want to add some custom HTTP headers onto a ASP.Net web service

Question

I want to add some custom HTTP headers onto a ASP.Net web service to allow cross site access.

the result I need is something like this. i.e,

HTTP/1.1 200 OK
Content-Type: text/xml; charset=utf-8
Content-Length: length
Access-Control-Allow-Origin: *
Access-Control-Allow-Methods: GET, POST, OPTIONS
Access-Control-Allow-Headers: X-Requested-With
Access-Control-Max-Age: 86400

<?xml version="1.0" encoding="utf-8"?>
<soap:Envelope >
  <soap:Body>
   .....
  </soap:Body>
</soap:Envelope>

I tried this but it doesn't work

<WebMethod()> _
Public Function SomeMethod(blabla...) As Something
    ...
    HttpContext.Current.Response.AddHeader("Access-Control-Allow-Origin", "*")
    HttpContext.Current.Response.AddHeader("Access-Control-Allow-Methods", "GET, POST, OPTIONS")
    HttpContext.Current.Response.AddHeader("Access-Control-Allow-Headers", "X-Requested-With")
    HttpContext.Current.Response.AddHeader("Access-Control-Max-Age", "86400")
    ...
End Function

I'm using Don.Net 2.0

any idea? thanks in advance.