How to use a disk-based-storage with different credentials?

• Backup Exec server ver 21.4
•  Windows server 2019 with domain (AD)
•  Backup Exec installed with a domain account and it's services are also started with a domain account. 

We are backing up a few server within the domain. Everything works!

We have a NAS which we have joined to the domain. We share a folder at the NAS with AD privilegiers and Backup Exec are able to create a disk-based-storage to //192.168.100.100/sharedfoldername, since the service account for BE have the rights to that folder. 
Simple and understandable. 

BUT. In case of virus/malware entering the system and getting access to the AD, the virus could easily infect even the backup folder at the NAS. 
To make it more difficult, we would like to remove the AD join from the NAS, setting up a local account at the NAS and let BE using theese credentials for the local user at the NAS to connect the disk folder. 

I that even possible? How do I tell BE to use different name/password for a disk folder?  Any workaround?

Thanks in advance

Best regards
Martin