Manually handle transactions instead of JtaTransactionManager

I am working on a setup with multiple databases, technology stack's spring with hibernate running on tomcat 6. Transactions across databases was not a requirement, and each database has its own dataSource, sessionFactory and transactionManager (org.springframework.orm.hibernate3.HibernateTransactionManager) with a declarative use of transaction management (@Transactional annotation). Recently there have been a requirement to have a one-off case of making insertions in two of those DBs (say db1 and db2) transactional.

I am aware that there are third party libraries like JOTM and atomikos, which can add JTA support to tomcat. But I would like to know if it's at all possible to manage transactions manually.

For example, can there be something like following?

Transaction transactionDb1 =     sessionFactoryDb1.getCurrentSession().beginTransaction();
Transaction transactionDb2 = sessionFactoryDb2.getCurrentSession().beginTransaction();
try
{
    // DAO layer call to DB1
    // DAO layer call to DB2

    transactionDb1.commit();
    transactionDb2.commit();
}
catch (Exception e) {
    transactionDb1.rollback();
    transactionDb2.rollback();
}

It probably wouldn't be as simplistic. But is something like that possible? As far as I know Programmatic transactional handling can be used. But how do I go about it combining with the declarative approach? Would I still be able to use @Transactional for other cases? Any help would be really appreciated.