You could either migrate or copy the job from the working volume to the final one:
... The term Migration, as used in the context of Bacula, means moving data from one Volume to another. In particular it refers to a Job (similar to a backup job) that reads data that was previously backed up to a Volume and writes it to another Volume ...
... The Copy process is essentially identical to the Migration feature with the exception that the Job that is copied is left unchanged ...
In case you are using software compression, it would be better to copy the volume files from one site to another (using migration it will decompress and compress again).
You can use RunScript in the job resource to run an rsync, ftp, scp or any other available copy method after the backup is done.
Don't forget to copy the catalog database, otherwise you'll need to use bscan or some to recover the information. You could use MySQL replication too.