Dalamser has released TimePreserver (http://www.dalamser.com/TimePreserver/index.html), an US $35 app for Mac OS X 10.5 and higher that lets you make archives of your Time Machine backups stored on a Time Capsule. A demo is available for download.
To user you attach an external disk to your Mac, run TimePreserver, and then store the disk away from your Mac and Time Capsule. Re-attach the disk and run TimePreserver to update the archive. You can use multiple external discs in rotation to provide extra protection. A minimum of two is good, always keeping one in a different location.
According to the folks at Dalamser, the advantages of using TimePreserver are:
° Complete archive of the Time Capsule without it being unusable for hours;
° Integrity of the Time Machine backups is protected;
° TimePreserver understands Time Machine backups unlike generic backup applications.