You can use Fiddler to catch requests that are being sent to and from the application and use it for debbuging. But you will be able to do it starting from 7.13.2 version of the applciaiton. Until that you can either create the functionality and then use it after the upgrade or create the request on c# via a script task element.
Both bpm'online and the service are in cloud, so I cannot use fiddler. What is the target release for 7.13.2?