It should be possible to acomplish what you want by putting your mysql-service.xml file into an .ear file and add a jboss-app.xml file in META-INF. The jboss-app.xml file should contain a reference to your mysql-service.xml file in a service tag. Example:
However, there is a bug in the EARDeployer that prevents if from recognizing *-ds.xml and *-service.xml. There is a fix checked into the main branch of EARDeployer in CVS but unforturnatly not to the 3.0 branch.