element in jboss-service.xml ... ?
It actually seems that the conf directory is already part of the classpath. Of course I couldn't tell because the code that needed conf to be in the classpath was within an initService() method and not a createService() method (I'm porting from 2.4.x). I was getting a failure, jumped the gun, and thought that it was a classpath issue. Sorry about that.
Also, the docs make it seem like the element is only used to load archives - it wasn't clear if the "archive" attribute could be left empty. I suppose it should be obvious but I had doubts.