HELP: Force REQUIRED transaction propagation

Hi,

I have a web service method which calls to many transactional methods of many DAO classes (annotated with Transactional(propagation = Propagation.REQUIRED_NEW)). I don't want these methods to create many new inner transactions and should use existing transaction instead. Is there any way to force reusing existing transaction without touching those DAO classes source code as I don't have access to the source code.

I'm thinking of overriding Spring JpaTransactionManager class to do so but it has all critical methods made final or private which immutable to changing (e.g. getTransaction(), handleExistingTransaction(), ...) --> HELP!!!!!

Thanks,
Tai