It should be possible to add AtomicActionExpiryScanner to the EAP 6 configuration as outline below:

 
<system-properties>
    	<property name="RecoveryEnvironmentBean.expiryScannerClassNames" value="com.arjuna.ats.internal.arjuna.recovery.ExpiredTransactionStatusManagerScanner\\s+com.arjuna.ats.internal.arjuna.recovery.AtomicActionExpiryScanner"/>
    </system-properties>

 
Unfortunately the value of the RecoveryEnvironmentBean.expiryScannerClassNames seems to be overwritten in the ArjunaRecoveryManagerService class. As a result there is no easy way of removing transaction manager debris from object store.