he can use $1 if, he runs his program like this:
./script.sh file.txt
now i haven't done scripting in a few months, but i think it'll work if you do it pretty much the way you had it.
ip = 56.142.565.451
user = "johnny"
pass = "passwd"
ftp -n << EOF
verbose
open $ip
user $user $pass
ascii
lcd /domino/notesdata50/prod/cantina_files
put $1
bye
EOF
echo "FTP Terminado"
then to run it, it'd be ./script.sh yourfile.txt