How will the duplicate command work with out connecting to primary or the catalog? The location of the backup files are based on where they were backed up to there is no way to change that unless you move the files and recatalog the new location.
From Database Backup and Recovery User's Guide at Duplicating a Database
In backup-based duplication, RMAN creates the duplicate database by using pre-existing RMAN backups and copies. This technique of duplication uses one of the following mutually exclusive subtechniques:
- Duplication without a target database connection, RMAN obtains metadata about backups from a recovery catalog.
- Duplication without a target database connection and without a recovery catalog. RMAN obtains metadata about where backups and copies reside from
- Duplication with a target database connection. RMAN obtains metadata about backups from the target database control file or from the recovery catalog.