Have you considered digging it up, and putting it in a pot?
I have done that before a hard freeze, and had some success.
Course, I have also picked the green fruit, washed and dried it, then wrapped in newspaper. It gradually ripened over a couple of months or so, and the taste was far superior to grocery produce around here.
I have it in a large pot now, and it is just a few feet from my tool shed which I can heat with a small heater.
BTW, does anyone need mimosa tree seeds? I thrashed about 100 beans this week and have plenty of seeds to give away.