How to find out the proxy on the client?

Question

C++ / C#

I have a server using callback contracts to communicate with the client. But how can I get the proxy server object in the function handler of this contract on the client to answer it? Is it possible somehow? I mean not just store connected, but how to find out dynamically, tk. I want to make that the client could be connected to several servers at the same time. Server proxies (contract objects) are stored in a list, but how can I find out from the callback contract handler which server the message came from in order to send a response to it?