The 5K answer is a bit of material and probably below the standard TCP window size of your OS. This means that even if you close your network connection immediately after sending the request and check only the first bytes of the response (to make sure that the request is really received), the server probably already sent you the whole answer, and the packets are already on the wire or on your computer.
If you cannot control (i.e. crop) what the server response is for your notification, the only alternative I can think of is to add another server to the remote machine, waiting for a simple command, and executing the real request locally and just sending back to you result code. This can be done very easily, even with bash / perl / python, using, for example, netcat / wget locally.
, - , .