Actually very simple. The web host lets his webspace via Confixx managed, offers cronjobs and each user can create his backups via 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 takes the automatic backups via Confixx.
