It would be very useful to the application server if there were an API method to register an interposed synchronization on a transaction that was not currently associated with the calling thread, the same way that non-interposed synchronizations can be. Right now the only two options are to use TransactionSynchronizationRegistry, which requires that the existing transaction be suspended and a new one associated, or to use reflection to directly call the registerSynchronizationImple method of the transaction. Neither one is optimal.