I applaud all the effort you are putting into saving this banana!
It sounds like those culverts have worked well for you in the past; and admire all your plans for stabilizing it (with water & cables) and attempting to deal with both heat and cold. I am guessing you get a lot of wind where you are. My first banana (Gros Michel!) also fruited just when the weather was clearly getting too cold for ripening (November here) and I was advised to feed it heavily with potassium and keep my fingers crossed. Of course, I live in SoCal so frost is rarely an issue but I still invested in potassium and Xmas lights wrapped around the 2" pvc pipe supporting the bunch and was able to harvest the bananas the following August.
I have little more experience with these guys than Sir Doofus so am reluctant to offer advice. But I agree with both of you that digging up a plant this big at this point would probably be a disaster.
I am currently growing both cacao and yang mei in the ground after starting them in a greenhouse made from 1" pvc pipe and clear plastic. Now they are under 90% shade cloth clipped to the same pvc pipe hauled out to the garden and rebuilt around my plants. I will be switching to 30% come fall and will probably be building something almost as tall as your tower for the cacao (which may well have been a mistake to plant but... chocolate!...how could I not???) Since you already have grown this banana successfully for three years in a greenhouse, I am sort of wondering about just building a temporary one around the IC in the ground, maybe with the same 2" pvc we use for supports.. or even your cleverly weighted down culverts Visual monitoring would be a lot easier. But again the stability in your particular wind/rain conditions could be a bigger issue.