Linux – Exclude mounted folders from tar archive

we want to backup our server and this seems to be pretty simple thing to do except one. Currently we use something like this:

tar cvpjf backup.tar.bz2 –exclude=/proc –exclude=/lost+found –exclude=/backup.tar.bz2 –exclude=/mnt –exclude=/sys /

Everything is fine, but we do not want to include mount points, as several ftp users has chrooted access to their homes with mounts like:

mount –bind /var/www/folder /home/user/html

Is the any way to exclude such folders from being backuped?