cron + lftp

peut-etre simplement en mettant le lftp avec l'option miroir dans un cron

toutes les heures par exemple...
le mode -R te permet eventuellement de recuperer automatiquement ce que tu aurais mis sur la freebox

visiblement lftp dispose des options interessantes pour toi
man lftp :

mirror [OPTS] [remote [local]]

Mirror specified remote directory to local directory.
-c, --continue continue a mirror job if possible
-e, --delete delete files not present at remote site
-s, --allow-suid set suid/sgid bits according to remote site
-n, --only-newer download only newer files (-c won't work)
-r, --no-recursion don't go to subdirectories
-p, --no-perms don't set file permissions
--no-umask don't apply umask to file modes
-R, --reverse reverse mirror (put files)
-L, --dereference download symbolic links as files
-N, --newer-than FILE download only files newer than the file
-P, --parallel[=N] download N files in parallel
-i RX, --include RX include matching files
-x RX, --exclude RX exclude matching files
-t Nx, --time-prec Nx set time precision to N seconds (x=s)
minutes (x=m) hours (x=h) or days (x=d)
default - mirror:time-precision setting
-T Nx, --loose-time-prec set time precision for imprecise time
default - mirror:loose-time-precision setting
-v, --verbose[=level] verbose operation
--use-cache use cached directory listings
--Remove-source-files remove files after transfer (use with caution)