If the rest of your application uses EJB or uses JMX, you should be able to pick out the object name and do depends against it. At the very least, you can make your own deployment orderer. (Refer to default/conf/jboss-service.xml)
You may also activate the PrefixDeploymentSorter (see conf/jboss-service.xml, commented out by default) and then name your .sar something like:
so that it starts last.