Scrum on very short projects?

Question

I'm using Scrum and really liking it. However, my shop finds itself in projects where the duration of the development effort is two or four weeks. We've already modified the sprint length to two weeks, and everyone here says "it'll be Scrum, just with one and a half sprints."

I don't think we can get a lot of value from one and a half sprints. How can we get the benefits of an iterative development process with only one, two, or one-and-a-half iterations?