Entity persistence and the persistence.xml file with the jettyRun task?

I’m using the Gradle jetty plugin to prototype a webapp at the moment. I’ve placed the persistence.xml file in src/main/webapp/WEB-INF/classes/META-INF/persistence.xml (as recommended, http://javahowto.blogspot.com/2007/06/where-to-put-persistencexml-in-web-app.html). When I use the jettyRun task the classpath is not setup correctly to auto-detect the (javax.persistence) entities.

What can I do to configure Gradle to use the correct classpath with the jettyRun task?