Getting yourself listed as a BMI songwriter & music publisher is a simple matter. All you need is a CD with your songs on it, send it to your local folk music programming (public) radio station, and have them program it. You might be able to do a short interview with the show's producer/host while he/she plays selections on the air. If you do that, you're in. All BMI wants to know is whether one of your songs has had air play. Once is good enough for them.
Jim