C# - Using SoapExtensionAttributes On Client Side With Async Web Methods?

I implemented custom soap extension and registered it into client application configuration file. It works fine.

(I would like to implement progress bar functionality like [URL]

But I don't like some thing - custom soap extension is invoked by every call of my web service. In order to fix this situation (call WS just by required methods) I implemented custom SoapExtensionAttribute like below:

[AttributeUsage(AttributeTargets.Method)]
public class CustomSoapExtensionAttribute : SoapExtensionAttribute
{
public override int Priority { get; set; }
public CustomSoapExtensionAttribute() : this (1)

[Code]....

I added this attribute to required methods of web service proxy classes (and removed registration into client configuration file).

My soap extension doesn't invoke when required web methods are calling. Anotherone, I don't know it is important or not - my required methods are async web methods.