Ran into this with a county in New York state this past week. They asked me to sign a form promising the list would not be used for commercial purposes. According to 18 USCS § 31 "The term “used for commercial purposes” means the carriage of persons or property for any fare, fee, rate, charge or other consideration, or directly or indirectly in connection with any business, or other undertaking intended for profit."
So, even operating without an LLC doesn't seem to get me where I need to be. The definition is pretty broad, and not really in favor of someone doing business. I'd still like to target that county at some point, but for the moment I have backed off.
As for getting rid of the names and addressing them all to "Vacant Land Owner" or something like that, it moves you another notch on the "Personalized mail / junk mail" scale, if you can live with that.