FYI, on the latest firmware, I just did it manually.

mkdir /home

edit /etc/passwd and add the user with 'x' in the passwd portion, /home/{username} for the home directory. You can either use groupid 100 (users, already in /etc/group) or add a group specifically for the user. (e.g. add user with id starting at 1000, add a group matching the username with the same id - probably a good idea to add the user to users also in the /etc/group)

Once the username is in /etc/passwd run:

passwd {username}
to set the passwd

mkdir /home/{username}

to create whatever you specified as the home directory, then

chown {username}.{groupname} /home/{username}

replacing the stuff in {} obviously with your values.
At that point, log out, log back in with the user in question. e.g. ssh myuser@myonion.local or whatever your ip is