External Storage -> user variable in share name

Hello Nextclouders,
we would like to get our SMB/CIFS Shares to work with Nextcloud.
Problem is, every user has it’s own share. When I try to use the $user variable in the “Share” Field it does not work. Is there any chance to get this working? Workaround or something like that?

Example:
LDAP users are loggin in to Nextcloud with last_name.first_name
Share should be last_name.first_name$ ($user$)