You should look beyond the standard outlets. The so-called "micropublishing revolution" is slowly emerging in mathematics and science in general. Original research ideas and results that aren't necessarily suitable for journal publication regularly find their way here on MathOverflow and in a variety of alternative outlets such as blog posts, social networks and whatnot.

The idea is not new, Doron Zeilberger's 39th Opinion was posted in 1999 and Michael Nielsen has already written several books and essays on the topic. Though these new outlets don't have the notoriety of journals and other traditional outlets, they all achieve the basic goal of disseminating research ideas. (A five-line proof doesn't need any peer review or any other "added value" that journals provide.)

Look around until you see something that fits your result. Don't worry about community acceptance and similar illusions, the people who are interested in your result will eventually find it and use it. News travels much farther and faster than it used to!