Yo fin :)
I'm assuming that the user mort is a user who will be using ftp solely to admin his web pages on the server, yes? I'm not sure where your users http files will be kept, but apache on my sys would keep them in /usr/local/httpd...
So I would create a user 'mort' in the group 'client' on the system and set his entry in /etc/passwd to something like this...
- mort:x:600:92:Client Webmin:/usr/local/httpd/mort/:/etc/ftponly
Anything like this will do, just setup the user as you normally would and make his home directory /usr/local/httpd/mort and change the /bin/bash entry to /ect/ftponly so he cant get access to the machine by any other means.
and set this line in /etc/ftpaccess
this will chroot the user to /usr/local/httpd/mort (so he is here but will not be able to move to a higher dir. ie he will see / only)
You will need to specify upload permission in the ftpaccess file as well as this is disabled by default (on more recent versions anyway) This is explained as are all the options (you'll want to setup some more options) in the ftpaccess man page.