Hi Rohan, a couple of thoughts are:
If application ZW is running on a supported platform and you have a CAI license, you could enable the agent to capture the webservice calls. Keep in mind though that you need to bounce the App Server in order to add the CAI agent to the JVM. This might be a non-starter since you say you cannot take the system(s) offline to make an endpoint change to point to the recorder.
Another option worth considering is to capture a pcap file of the traffic coming into/out of ZW. If ZW is running on a Windows server, you can do this using a tool such as Wireshark. If Linux or Unix, you might need to run tcpdump. Using the .pcap file created by a tcp packet capture tool, use the create VS Image From PCAP option to build the service.
If ABC and ZW are using SSL, it will be more challenging because the payloads will be encrypted on-the-wire. You can apply some configurations to Wireshark to identify the keystore to convert the request / response into clear text, but I have had difficulty with this setup in the past. I have never tried SSL with tcpdump so I cannot say what the possibilities are.