I made this automator action to instantly change the extentions RAR and ZIP to CBR and CBZ. Put this app in your dock, and drag your files to it (all of them at once is fine, mixed RAR and ZIP is fine too) and it'll launch automator and do the rest.
Although CBL can read files with the rar or zip extensions, if you double click them at first, they will usually unrar/unzip. This will make them "native" to CBL, you'll see the icon change instantly to CBL.
I couldn't get the "attach file" to work, so I uploaded to megaupload.
For those of you who haven't used it, you don't have to register or anything, just type the 4 letter and number combination at the top right, click download, wait 45 seconds while staring at the horrid dating ads ( - _ -;) and then the download link will appear.