I found instructions for creating a custom ISO for Backtrack 4 using a program from http://www.linux-live.org. Essentially, you build the system they way you want it, create a work space, then use the script from linux-live to package it. Note that I have not (yet) tried this on a 'normal' Ubuntu install, however BT4 is an Ubuntu-based live CD. I have made a custom BT4 CD including Nessus.

The instructions are in the BT4 wiki n(undetr documentation at http://remote-exploit.org - I can't get there from this machine or I would provide a complete link).