I released a shell script borne from my attempts to remaster Ubuntu 14.04. Tested in VirtualBox! You must have root and an ISO to remaster.
Get it here: https://github.com/beta0x64/remaster.sh
The command is used like so:
./remaster.sh original_official_iso.iso new_custom_iso_name.iso
First, it will attempt to update your system and install squashfs-tools.
Then, you will be dropped down into a terminal prompt inside of the ISO where you can use apt-get to install whatever you want.
Just type “exit” when you are done, and it will continue to write your changes into your new iso file.
At some point, you’ll be entered into nano where you can optionally change the DISKNAME which appears when the USB device is plugged in, for example.
When you’re done, use sudo to remove the livecdtmp/ directory.