Since you don't have static IP addresses I assume that you have your home network behind a hub/router or switch to share out the net connection and that this router is providing a NAT so that the machines on the inside get IP addresses.
All you need do is get the NAT to not serve out a couple of IP addresses, usually at the bottom of the range, and put a DNS server and KDC on the 'net manually configured to use the addresses rather than ask the NAT for one.
If you don't want to keep a second server just as the DNS then set up the machine that will have the KDC so that it is its own backup DNS. Then when you remove the first DNS it will still work.
Of course you have to have at least one permanent computer on the 'net, but you're going to need that for shared home directories anyway.
If you have any trouble configuring the DNS I suggest you read the Linux Network Administrator's Guide for the section on
bind or the O'Reilly book.