Indeed, thanks for the reference to that JIRA. AS6 btw also has this feature (it's in Java EE 6 afterall), only there it doesn't completely work. The data source is created, but inserted into the wrong JNDI location.
I created this issue for it: https://issues.jboss.org/browse/JBAS-8816
Do you know whether the JBoss specific configuration file can be used in an EAR like was possible with the -ds.xml files? The Java EE 6 standard way is certainly usable, but the JBoss specific one seems richer.