A multi trip policy would cover you surely? As in 'your non refundable trip' may start from New York, but before you start that, you are flying Boston to New York. As far as the multi trip is concerned, it is all 'travel' isn't it?

Last year, I was travelling by train for a couple of hours to an airport, bad winter storms hit, and I was worried, but this was in my multi trip policy:

Trip cancellation / interruption, provides for rescheduling etc if...
"You miss a connection or must interrupt your trip because
of the delay of your connecting passenger plane, ferry, cruise
ship, bus, limousine, taxi or train, when the delay is caused
by the mechanical failure of the vehicle, a traffic accident, an
emergency police-directed road closure or weather conditions.
The vehicle must have been scheduled to arrive at your point
of boarding at least two (2) hours before the scheduled time
of departure."