Boston Tower regulates the traffic over that area but you would have to catch it between departures/arrives on the two tower frequencies (there are three tower frequencies including the Boston Skyways frequency). I have heard Metro1, 2, etc, and Fox 25 helicopter during rush hour requesting clearance into the airspace.
They may also have a separate frequency for helicopters that they use to talk between each other. I have heard helicopter pilots again during rush hour times mention that they are talking to the other pilot on another frequency.