I thought counties were pretty much irrelevant in New England, or at least in Massachusetts. When my folks lived in Belchertown in the early '80s, they were in Hampshire County but it didn't mean anything. All the towns were one after the other (Belchertown to Amherst to Northampton going west, for example), and there were no "unincorporated areas" or "county islands" like there are in other parts of the country.
Couldn't the individual cities and towns petition the FCC to move their market assignment from Providence to Boston? Your situation is also a good argument to scrap the idea of single-city markets. Why not allow both Boston and Providence stations onto the cable and satellite systems? They can't stop people from watching stations in both cities if they can be received, so why not?