I finally found a Workaround for my problem.
iDA in question is SAPonOracle.
Some backups also use NetApp OpenReplication w/ SnapVault, therefore I have to use the same StoragePolicy for all Backups targeting the same NetApp Volumes.
But I created a seperate subclient, and activated backupcopy for all jobs in the SP, but associated only the subclients, where BackupCopy is desired.
Now the majority of backups (Snap and Logbackups) are created as "command line" and backups, where a backup copy is required, are triggered using "qoperation execute" script from the client.
Not that I think this is a good solution, but feasable for SAPonOracle (or Oracle), since multiple subclients addressing the same content, can be configured.