Quick notes:

1/ Download iso from http://releases.ubuntu.com

2/ Install UCK:

sudo apt-get install uck libfribidi-bin

3/ Start uck-gui:

– Choose languages en/en
– Choose default deskop: Unity
– Remove windows files: yes
– Hybrid: yes
– Customize?: yes

Let it build and then when possible you will have the option to customize via console.
In that console just remove all LibreOffice packages (Don’t worry, you can install them later after you install Ubuntu):

dpkg -l | grep -i libreoffice | awk '{print $2}' | xargs apt-get -y purge
rm -fr /var/lib/libreoffice

Then exit the console window (ctrl+d) and let it continue the build.

In the end you will have an iso of about ~600MB:

$ du -hs ~/tmp/remaster-new-files/livecd.iso
575M	/home/x/tmp/remaster-new-files/livecd.iso