I was looking around the other day at the Freedom Scientific site and saw that they have JAWS 7.0 for USB Thumb Drives... Thought that might be a valuable offering on the site. For either visually impaired users or for application developers trying to make their applications more accessible. Here is the URL: http://www.freedomscientific.com/fs_downloads/jaws.asp
It is not portable. You just carry your settings with you.
To top it all off, it is not open source(it is not even free).