I was chatting with a colleague about this, and she made the great suggestion to try splitting the question into two: "Do you agree or disagree?" THEN (essentially) "Strongly or weakly?" With computer-based questionnaires, at least, this is easy to implement, and likely would be faster (I suspect) than puzzling through the whole spectrum of choices in one go. I'm going to try it out in an upcoming pilot. Let me know if you do!