I couldn't find this on the the JBoss wiki although it's supposed to be there, somewhere, not that I looked really hard, but then again I shouldn't have to.
In your JBoss deployment directory usually $JBOSS_HOME/server/default/deploy edit the ejb-timer-service.xml file.
Find the Noop line and uncomment it, and comment out the lines after it that describe the DatabasePersistentcePlugin. This is pretty handy for development, but not recommended for production.
<mbean code="org.jboss.ejb.txtimer.NoopPersistencePolicy" name="jboss.ejb:service=EJBTimerService,persistencePolicy=noop"/>
You should be able to do this without having to restart the server. Finally you can check via the jmx console to verify that everything is good to go. under jboss.ejb – the persistence policy should read:
Finally I should add the JBoss team needs to develop a nice programmatic way for querying and purging timer requests, as it stands now it looks almost impossible outside of building a custom mbean, which is probably what I'm going to have to do for the stuff I'm working on to go into production. It shouldn't be this hard.