What Andrew means is that you can't do any substantive research in a four week span. You might be able to get your name on a poster/pub, but only as a token. If you want to say you really did something, do a case report as Andrew suggests. It will be a broad learning experience on a relatively specific subject and will provide you a topic you can discuss with some degree of expertise on the interview trail. Taking a year off to do research is a little extreme, unless you're REALLY interested in research.
There are 4 week research electives to be had, no doubt. To be honest, I did one; however, I was working with my old grad school advisor, so I pretty much picked up on a project I had worked on as a doctoral student. The learning curve is just too shallow, if you aren't already familiar with the lab/project.
Best of luck!