Having spent 40+ years in broadcast newsrooms, that's a fine idea, Joseph. Technically, it would be quite easy. If master control for WGME was moved to WBZ (this is increasingly common---"hubbing" master control facilities for multiple markets), a story could be produced for WGME every day that would be automatically inserted into a specific block of WBZ's newscast as it went to Portland. WBZ's viewers would see local Boston stories while WGME's audience would, for those few minutes, see a story or stories about Southern Maine.Quite possibly, with the repeaters/satellite stations each maintaining small news bureaus that would shoot some news footage and feed it back to the parent station to air on local newscasts seen on both the parent stations and all of their repeater/satellite stations.
How it could work:
Let's assume that CBS owned WGME-13 in Portland, Maine and made it a repeater/satellite of WBZ-4 Boston. WGME would simulcast WBZ's local newscasts, but would also have a small news bureau that would cover one or two stories from Southern Maine each day, feed them to WBZ, and in turn, the story (stories) would appear on newscasts produced by WBZ and seen on both WBZ and all it's repeater/satellite stations.
Why not just air the Portland stories on WBZ? Thirty-five years ago, I had News Directors telling me that stories of interest in the third-largest suburb (200,000 people) of the large market we were in (1.6 million people) was not gonna play because the people in the rest of the metro didn't care. If something caught fire, if a kid were run over by a school bus, if there was a psycho on the loose in that suburb---THAT we'd air. But non-sensational stories of value to people who lived there? Pass.
Also, WBZ would not go to the expense of having employees or a bureau in Southern Maine. So what ends up happening is WBZ would just pipe its Boston newscast into WGME, folks in Portland would get used to saying "We get Boston TV news up here" and when something really bad happened in Portland, 'BZ would send a crew up to cover it. Or hire a local stringer on per diem if they could get away with it.
It's a shame, but it's how that would most likely go.