That’s indeed currently not possible. Making the BpmnModel Serializable is not enough, as the behaviour (and to a lesser extent, the EventSupport with EvenListeners) is stored in the BpmnModel too. A lookup should be needed when that is null … but that logic is currently in the parser logic…
Anyway, I saw you created an issue (https://github.com/flowable/flowable-engine/issues/481), we’ll look into it and discuss it there. Thanks for reporting!