How to pre-install CPanel behind a NAT

When you co-lo your box and get your ip, no-one except you will know the new ip and the chances of getting hacked imho are exceptionally low! If you are really worried then setup a firewall meantime and only allow port 22. You are also unlikely to get hacked if your root password is secure enough, so choose a good one.

As far as "pre-installation" goes, there isn't really that much of a point. You can complete install at home without having an external ip it just wont work if you try to setup whm because you need the license server to have external ip.

And as for reboots, there are no reboots required when installing cPanel/whm. Even if you had to you could reboot via ssh/telnet with 'reboot'.

Hope that's some help