[jboss-as7-dev] Parameterized config of datasources in standalone.xml

I'm working on parameterizing my datasources in standalone.xml. Specifying system properties as ${DB_URL} for connection url, username, password works great using properties passed to jboss via -Dapp.properties, but after the first run, the values are permanently substituted in this file. If my external property file is changed, standalone.xml no longer picks up the change. To re-substitute, I have to get the initial version from the standalone_xml_history dir and overwrite the current version. Is there a better we to handle external configuration of datasources and if not, is there a better way to reset the standalone.xml config? Thanks, Rick