ASMX Web Service Soap Extension - How to inject an attribute into a client proxy class?

I am trying to set client side soap extension attributes. For example:

Implementation in web service:

[AttributeUsage(AttributeTargets.Method)]
public class EncryptMessageAttribute : SoapExtensionAttribute
{
    private string strKey="null";

    public string StrKey
    {
        get {  return strKey; }

        set { strKey = value; }    
    }
}

      

        
        
        
      

    

Soap extension class:

public class EncryptMessage : SoapExtension
{
...
}

      

        
        
        
      

    

Used in web method:

[WebMethod]
[EncryptMessage( StrKey = "pass")]
public string test2()
{
    return "ok";
}

      

        
        
        
      

    

Implementation in the Proxy class:

[System.Web.Services.Protocols.SoapDocumentMethodAttribute("http://tempuri.org/test", RequestNamespace="http://tempuri.org/", ResponseNamespace="http://tempuri.org/", Use=System.Web.Services.Description.SoapBindingUse.Literal, ParameterStyle=System.Web.Services.Protocols.SoapParameterStyle.Wrapped)]
[EncryptMessage( StrKey = "pass")]
public string test() {
    object[] results = this.Invoke("test", new object[0]);
    return ((string)(results[0]));
}

      

        
        
        
      

    

Soap extension attributes: [EncryptMessage ( StrKey = "pass")]

I want to set the client side soap extension attribute before using Soap extension when I call some web methods.

Example: I am calling some method that sets the soap extension attributes on both sides before the soap extension is used. Can anyone help me?