Between Fedora 12 and 13

It is fairly easy. As an example of custom Fedora Remix, feel free to take a look at

http://omega.dgplug.org/11/Live/i686/Omega-11-i686-Live.ks

Since the alternative kernels you are talking about is part of a repository, you can simply point to it within a kickstart file. Third party repositories usually have the repository files as part of foo-release that needs to be added to the kickstart file and software updater will be able to pick up updates easily. Gobuntu doesn't actually exist anymore btw and Fedora Project is unlikely to be interested in maintaining any kernel variants.