Welcome! And welcome to
@James Pease as well!
First, I would argue that the exclusion of widows "married more than once" is a misrendering. Paul rather commanding that she had been a faithful wife, regardless of the number of husbands. I think that this is both grammatically sound as well as contextually supported--for example, what would we say of the Christian woman who was once a "younger" widow who now finds herself widowed-again but now 'beyond the age of marriage' (a state not at all unheard of). Well, she was to 'be enrolled.' As a related aside, this was the genesis of what-today we call deaconesses--older widows who were taken care of (headship under overseers and deacons, food, clothing, shelter) by the church and thus devoted themselves to service "mercy works" such as making clothing, caring for the sick and young orphans, etc. Of course, as with so many things, this would eventually come to be corrupted by asceticism and eventually be joined to the concept of monasticism.
Anyway, to your question, your idea is not hogwash. In fact, quite the opposite. What Paul had in mind with older widows was a kind of welfare. They were provided for and so turned their hands to a rather unique and beautiful service to their congregations and communities (remember that orphanages, hospitals, soup kitchens, etc. did not exist at this time).
Now, as far as nuts and bolts here, polygyny is neither commanded nor forbidden (it's an "adiaphora"); while marriage can be argued to be a commanded estate (1 Cor 7:2), but I'm not entirely convinced of either side of that argument at this time. Nevertheless, because we're in the realm of adiaphora here, I think you're hitting the nail rather squarely in its head.
IF we are to care for the widow and the orphan (which would include covenantal widows and orphans), and there IS a commanded mechanism to do so for the 60+ year old widows, then it falls upon the people to directly provide this care. Hence, while I would argue that polygyny and/or adoption BEST meets this care, I don't think we can charge folks with being sinful by exercising other means (that is, to not marry/adopt them but still otherwise provide).
To be more specific, in my opinion, the best advice to them is 'get married.'
Ah, but that's the real rub, isn't it? Convincing them (and our men) is proving...an interesting endeavor--at least for me.