If you only use one watt, on what appears to be an empty part of the frequency, it's unlikely that you will cause much trouble with a commercial station. You would likely hear any station that would potentially be bothered. I still would keep it to under a half-hour, just for safety's sake.
You could announce HF Underground's URL on the air, and have listener's post logs on the "FM Free Radio" forum. Or, get a Gmail account, and announce that over the air. The latter has the advantage that they won't have to register to use it.