Thanks.
The newish 3.1 release of CCC includes incremental backups.
See MacWorld.
http://macs.about.com/od/applications/gr/cccgr.htm "CCC 3.1 also offers file-by-file copying, which can still create a bootable clone. This option can also perform incremental backups, allowing you to keep the clones up to date, an often-overlooked aspect of using clones as a backup method. In the past, it was necessary to download and install a separate application to use with CCC, in order for incremental backups to work. CCC 3.1 has a built-in synchronization tool, which is a big step forward for ease of use."
The new release uses rsync 3.0.0