All writers have coveted markets that they have been struggling for weeks, months and/or years to break into, and maybe you can, by writing something other than short stories . . .
Reviews: This is a great secret I think goes untapped for many fiction writers, which is unfortunate because fiction writers are some of the best reviewers. We know how to deconstruct a book’s plot, characters, and arcing theme, and we can spot strengths and weaknesses usually better than in our own work. This link provides an in-depth process to writing a review: http://writingcenter.unc.edu/handouts/book-reviews/
Non-fiction: This may seem like a leap if you have only ever written fiction, but penning in other forms may not only strengthen your own, but open doors to untapped talent. Instead of reading Poe or Verne for penning inspiration, why not write a biography of them instead or detail the impact of self-publishing on genre fiction today. With enough research, anyone can write a compelling article. Here is a pretty good link: http://www.wikihow.com/Write-Articles
Essays: Want to really exercise your pen? Try writing an essay about why the Book was better than the Movie, or what you believe will be the next big genre and why, or why being a panster might have drawbacks/benefits to being a plotter and use famous authors as examples (ex: King is a panster, but Rowling is a plotter).
Also, many writers have interesting and diverse backgrounds and life experiences. If you have ever worked in the court system, than you probably have some credentials to support your assessment about the legalities in legal thrillers. Here’s a link that provides some nice examples: http://www.monash.edu.au/lls/llonline/writing/general/essay/1.xml
Interviews: Know someone who has just published with a reputable press or has won an award? Ask them for an interview. Authors love to have their work noticed. I found this website to have the most ideas for interview questions. http://lawrencewray.wordpress.com/author-interview-questions/
Even though these categories are not truly representative of your fiction writing, it shows that you are an adaptable writer, that you are serious about writing and knowledgeable about other aspects pertaining to writing in general, and if accepted into that coveted market, may even spark a more serious review of your fiction work next time you submit.