There is a programme called Reconstructor for this purpose. It should be in the
repos or from here: http://reconstructor.aperantis.com/
I have never used it. It is for Ubuntu I believe. See:
http://en.wikipedia.org/wiki/Reconstructor

There is also this project: http://www.linux-live.org/

This one has much promise:
www.pendrivelinux.com/.../