None, currently it is not possible to store the encryption key in a different location.
Password Manager uses keys stored in local.storage to encrypt and decrypt data. To protect the keys we use Microsoft DPAPI to encrypt the keys (More info can be found):
This ensures that no other user can decrypt the key other than the user who created it being the service account. Even if this file was copied to another server you would need the correct user name and PW for the service account make it work.
Enhancement request 247109 has been created.
Our product management team reviews open enhancement requests and considers them for inclusion in a future product release. There is no guarantee that a specific enhancement request will be implemented in a future release. Please refer to the "New Features" section of the Product Release Notes for a complete list of Enhancement ID's addressed in the new release. These are available in our Documentation section of the Support Portal.