I use this tool:
http://www.cgsecurity.org/
Note that when using on a Kindle USB storage or an image file of a Kindle USB storage, when the software asks if the DOS partition table is a 'Vista' style table, answer: Yes
The Kindles use a rather non-standard set of formatting options.
@GM: PM NiLuJe - I think he has a demo.bin from his PW2.