Actually very simple way. The web host's web space can be managed via Confixx, offers cronjobs and each user can create his backups by Confixx.
Why it is now possible to play while backups directly to a set of user ftp, but no automatic configuration (a la every week a full backup) is possible, I do not quite.
After a bit of Google, the matter has been sorted out too, for a simple PHP script that takes the automatic backup by Confixx.
