Actually - it is very easy.
Don’t download Comodo Internet Security. Just download Comodo Firewall.
You can do so by simply reading the options on the Comodo website or following this link:
http://www.comodo.com/home/internet-security/firewall.php
This doesn’t come with any of the AV components at all. It only comes with Comodo Firewall and Defence +.
Yes - even when you choose the Firewall Only option Defence+ is installed - however it is automatically disabled so you don’t have to worry about it configuring that side of it. Plus it doesn’t get in the way when you are doing all that initial work in configuring the firewall.