While this is certainly a problem with how our current evaluations are set up... I'd say that this behaviour is more a side-effect of the fact that we're abusing meta to run these evals rather than a defect in the vote fraud detection. This is a very, very narrow edge case. Aside from these evaluations, I can't think of a legitimate case for one person to post a lot of answers to the same question.
On a main site, it's likely that if a person posts multiple answers that they are (or at least should) offer some sort of a different perspective, so legitimately serially upvoting all of them wouldn't make a lot of sense. In a way, the vote pattern analysis already ignores votes done on the question and its answers since the answers are from different people.
On a meta site, even for a question that's basically a poll, it is better to allow the community to post answers instead of having the same person prepare the question and the possible responses. The latter tends to stifle community participation as people feel discouraged from weighing in with their opinions instead of just voting on the pre-set answers. This is harmful, especially if those opinions aren't already captured by the existing answers.
Even though meta posts (on SE 2.0 metas, at any rate) don't affect reputation, voting still carries meaning. Mad Scientist nailed it in this comment: targeting a user on meta isn't any more acceptable than targeting a user on a main site.
So all in all, we will not be making changes to make meta a special case or otherwise support these epic site evaluation hacks. Instead, we're looking at how we can use /review to make these site evaluations more useful, natural, and easy to do. Stay tuned for more details on that in the customary 6-8 weeks.