I personally use static IPs on my home LAN. It makes sense in this scenario with lots of little gadgets like cams and tablets where I might want to telnet or ftp, and don't want the IP bouncing around.
You can definitely mix DHCP and static IPs. The normal way is to set a specific range on the DHCP server and just avoid that range for the static IPs. I set up a small range of 10 IPs.
Here is a windows DHCP server:
http://sourceforge.net/projects/dhcpserver/
I won't try to justify Kobo not being able to set a static IP. My android tablets have this ability, and even my two fairly low price webcams have this ability.