Delaying HTTP request phases using FiddlerCore

Question

I am using FiddlerCore to test out my applications behavior when waiting a long time for server response. I am using c++ winhttp.h library in my app. I am trying to introduce delay before triggering each async callback. So far I have tried two solutions:

1. Adding oSession["response-trickle-delay"] = receiveDelayinMillisecPerKb; as explained in this blog post, and this simulates slow streaming from storage detectable when WinHttpReadData is called.
2. Adding Thread.Sleep(delayMs) in different fiddler session state handlers (BeforeRequest, RequestHeadersAvailable, BeforeResponse, ResponseHeadersAvailable) but from my app it seems that all of them prolong the time between WinHttpSendRequest method and WINHTTP_CALLBACK_STATUS_SENDREQUEST_COMPLETE status callback.

Is there any other way to introduce delay in request in different request states using Fiddlercore?