C++: Is it possible using callback function with ncacn_http and rpcproxy server ?

I have a remote procedure and I can call it using http over rpc. I pass trough an rpc proxy server for arriving to my rpc server.

But I cannot call a callback function to my client inside the server function.
 
Is it possible using callback function with ncacn_http and rpcproxy server ?
 
We are using IIS on windows server 2008 R2 and the server rpc and the client on the same PC with rpc rpoxy.

If I use ncan_ip_tcp all works fine.

Thanks
Gianluca