In the meantime I managed to figure it out, thanks to the following articlehttp://middlewaremagic.com/jboss/?p=1081
The catch is simple: Just add the jboss-deployment-structure.xml file to the META-INF directory, with the following content:
<resource-root path="_path_to_archive_goes_here_" />
That's it. Jboss will add the resource specified to the classpath of the deployed SAR archive. Hope this helps somebody.