The runtime persistence is (somehow) pluggable, at least the http://locademiaz.wordpress.com/2011/02/07/drools-persistence-on-top-of-hashmap/ blogpost shows the way.

But the only way how to change the persistence for the HT service from JPA to something else (e.g. JCR) is "hack" EntityManager & EntityManagerFactory (in fact to write own JPA provider).

It'd be great to have a better way (e.g. the same as for runtime).