I thought about making ad/tracker blocking hosts file for the KT, it wouldn't be hard.
I wanted to ship something simple first, but I might put one together for the KT, unless someone else beats me to it.
The vanilla hosts file is just "127.0.0.1 host localhost.localdomain localhost localhost localhost.localdomain" and I added my line right below.
If you know your way around a *nix/OSX command line:
# mkdir etc
# editorofchoice etc/hosts
# tar czf KoboRoot.tgz etc/hosts
Then copy KoboRoot.tgz to .kobo. Keeping proper permissions would be ideal, but don't sweat it.