WCF log to IIS asynchronously

I have a requirement where I want to log the response of WCF method to IIS log against the current request. This is currently implemented but the problem is I have to serialize response object before logging it as AppendToLog method only takes string input parameter and this serialization taking most of the time. This is adding significant delay to the overall response time.

I want to understand if there is any way I can do this logging after I return the response to client ? I tried to do it asynchronously just before the return statement but this is not working as Current Context goes null.

Please let me know how can I solve this problem