I worked no magic on that, Nick. I simply installed U 12.04 via the ChrUbuntu method, then as soon as that was installed I went to Synaptic and installed K 13.04. It was just THERE. I didn't add it, I didn't tweak anything, it was just there.i heard Synaptic can install distros on top or in replacement of another distro, at least, that is implied by Moody who can get Kubuntu 13.04 on a Chromebook when the only supported (officially) distro is ChrUbuntu 12.04 LTS
Have you looked in your Synaptic? And do you have its settings to "Always prefer the highest version"?
Under Settings | Preferences | Distribution | Prefer versions from:, what are your choices? Although I did not fiddle with that at all--I simply did what I always do, set "Always prefer the highest version,"--I'm looking at it now and see both Precise and Raring among its choices. You should, too.