Offline backup of sites

I work on a project where there is need for taking offline backups of the sites hosted in boa in the client's inhouse server. The clients in-house server cannot be reached from the boa server. Before installing boa, the client directly accessed the mysql from his office and took a backup every day. The same way, files we also taken backup.

With BOA, I am unable to give the client two details
1. Db username and password
2. Document root of the website

Because both of these change automatically as and when the site is migrated to different platform for security updates and other stuffs.

The only way I see this can be achieved is that the client runs a bash script on his server which login to the boa
1. to read the nginx config file for the domain to get the documentroot and
2. then using the now available document root, read the settings.php to get the db details of the site
3. then using both these details take a backup of the files and db.

Is this a good way to approach this? are there any better ways to do the same thing? I am looking for someone to write the entire code for me, rather, if someone can point me in the right direction I can get into code and contribute back here.

thanks for your time.