This article builds on the build system that I've already provided so I'm only going to show the additional parts that need to be added.
First a path element needs to be defined. This will will store the locations of all of the additinal jar files that should be added into the war file. In this example, just one extra jar file is packaged, myextralib.jar.
Second, all of the files defined in the path element above need to be assembled into a single directory.
Last, a zipfileset element is added into the module element of the jwsc task. This is where the jar files get packaged into the war file.
A quick and easy addition. Enjoy!