I've added a "mappingResources" property to LocalContainerEntityManagerFactoryBean, pointing to orm.xml like files in the classpath. Note that those are not Spring location values but rather classpath resources, similar to the same-named property on the Hibernate LocalSessionFactoryBean. They will be merged into the default persistence unit, just like "packagesToScan" entity classes, and can also be combined with "packagesToScan".
JPA insists on those file names to be classpath-relative resources, so a URL-based approach won't work in a portable fashion. This is a problem with the Spring Data JPA approach, as far as I can see, since classpath scanning will return URL resources, not classpath-relative locations. This might work with some JPA providers but it won't be portable (to the best of my understanding).
So with LocalContainerEntityManagerFactoryBea, we expect "mappingResources" to be fully qualified classpath resources a la "META-INF/mappings.xml" or "com/mycompany/repository/mappings.xml". Enumerating them shouldn't be too hard in a typical application; as per the above, we do not support patterns there.