You can't. But you can give access to "ftpuser", and only for him, with the command
setfacl -R -m u:ftpuser:rwx /path/to/dir
setfacl -R -d -m u:ftpuser:rwx /path/to/dir
This requires group write access on this dir, which can be set with the command
chmod g+w -R /path/to/dir