I have more than one user on my vps, each one in a different sftp jail.
AFAIK to use the upgrade option without being asked for the ftp credentials are:
- add the ftp credentials to the wp_config.php file
- change the FS_METHOD to 'direct' in wp-config.php
- change the owner of every file to the one that the webserver is running
So, there's some way that can work when you have a lot of different users and you rather don't give the ownership of his/her files to the webserver's user? (obviously editing each wp-config it isn't a good idea either).