Rope around another nearby tree is an easy and efficient prop. Most of mine grow between coconut palms. I just throw a rope a bit higher on the coconut trunk than the banana, and clamp it taut, near the top of the banana stem. I include multiple stems in the same rope so there is tension between all of them, if there is more than 1 in the clump that are fruiting. Prevents wind damage during storms, and results in ripe bananas! Although it's not impossible, you're not describing pest issues - it sounds like it's purely a case of the fruit being too heavy for the stem. Particularly if you have other taller trees nearby, it's a very cheap and easy fix. In places like this where the soil is very difficult to penetrate because it's mostly coral rock, it's way easier to use rope than to try to drive something into the ground.