Most academic physicians are drawn towards applicants who want to be like them--namely, academicians. In truth, even the most academic programs (with the notable exception of Johns Hopkins) rarely see more than 50% of their graduates pursue academic careers. But demonstrating that you are interested in academics, and, at the very least, willing to give it serious consideration, is an absolute must.
By far, the best way to display your interest in academic medicine is to do research. It is not a must, and for some people, it is simply not a possibility; however, there is no question that it helps substantially. High quality basic science work is great--if it has some relevance to Urology, even better. Clinical projects with Urologists (these can be done at the end of your third/beginning of the fourth year) are looked upon very favorably. These small projects can also yield very strong letters of recommendations from influential people. Bring the topic up with any Urology attending, and you will be surprised how fast you can come up with a project that you can work on during an easy stretch of clinical rotations. Even clinical projects outside Urology will significantly improve your application. See an interesting case? Write-up a case report! Just let the attending know you want to write it up, go over it with him/her, and submit it to a journal. By demonstrating your interest, initiative, and follow-through, you will get yourself noticed. In addition, taking a year off to perform research is an option, as there is no question it will help your application to some degree. Obviously, this is a major commitment, however, and is only worthwhile if you are truly interested in taking a break from your clinical training. The strongest applicants have substantial lab projects (and publications) completed in the first two years, coupled with small clinical projects performed over the latter two years. Research conducted prior to medical school is also extremely relevant to your application. It should be stressed, though, that although research is a great plus, many applicants match at top programs without any research whatsoever.