I'm also in MA and if you decide to use a provent just make sure you keep it accessible. If you got caught by an inspector then you would be forced to remove it and find a way to legally vent you're bath. A lot of times in this type scenario we go thru the back corners of closets and find a route.
In other parts of the country I see plumbers talk about Studor vents I guess they are legal and roof penetrations are not required. I think those vents would only be available around here thru mail order.