We had this discussion on our flying group quite often and we always ended in "forget it". The legal issue with official ATC being broadcasted is so complicated that you as a private have no chance to fetch the legal implications (Btw pointing to liveatc does not help as this broadcast is not to be compared with a broadcast at a private event).
But why transmit the ATC frequency with all its legal implications? We usually ended in getting an exempt together with a temporary issued frequency special for the event. In the papers to file for the temporary frequency there usually is a paragraph addressing the issue. The "smoke on" stories from speakers are typically special event frequencies.