AFAIK you have to replace jBPM's ObjectFactory by a Factory using the SpringContext to resolve object names. I know you are using jBPM 4.x but maybe you find some inspiration on how to make jBPM use a SpringObjectFactory in this tutorial for jBPM 3.2:
http://www.jorambarrez.be/blog/2009/04/17/integrating-jbpm3-with-spring-part1/
With respect to the tutorial you would need to create a SpringObjectFactory (implementating jBPM's ObjectFactory) and instantiate the factory via Spring. Then pass the ObjectFactory into the Configuration bean.