Interesting use-case. If you are bound to only using the commandline then i would try to loop it with different output folders as the testrunner does not really support multiple-projects.
however
I really think you should utilize maven in this case. Because redfish4ktc2 has had the usecase for multiple project files before and created a maven-soapui-extension-plugin that has the test-multi goal.
Go have a look:
https://github.com/redfish4ktc/maven-soapui-extension-plugin
I think it would solve your use-case perfectly, and Jenkins can absolutely build using maven, there are plugins for it.
If you need guidance on maven then just give a shout and i'll set something simple up.
