find a way to enclose it in a temporary "greenhouse" when it is close to freezing, and put a heat source inside - even a light bulb gives off heat. If it gets frozen, it is over. Trim back the leaves if you have to, but keep it warm.

Cut off all the leaves and wrap bottom 7' of trunk in a electric blanket. It will take 3 months for a bloom to ripen. check temp under blanket keep at 70 to 80 f

Here is a link that might be useful: banana growing info