i managed to replace the default jBPM Runtime (pointing to ./runtime directory of jbpm full installer) with my own custom one pointing to an empty dummy folder and everything works fine - as long as all the necessary dependencies are present at the java build path.
Seems like a work-around rather than a recommended solution - but it works.
Still - i lack deeper insight and would very much appreciate any words of wisdom on 'jbpm runtimes' :)