This time of the year where I live, it takes forever to promote overripening of bananas due to the much cooler weather outdoors. Where in the summertime, a bait bag placed out in the sun with a fresh banana that isn't even overripe is ready within 5 days, but it might take several weeks this time of the year.
Last season, I read online that one way to fast ripen bananas was the bake them in the oven at close to 300 F for about an hour, or watch the skin until it turned totally black. This seemed to work, but when I tried to use as bait they would not ripen any further (in other words, they didn't seem to rot), rendering the bait useless. My guess is that baking halted the natural process that would have occurred somehow.
Recently, I tried a simple heat lamp and kept the temperature similar to what it would be in the car, around 120 -150 F. Took longer than the above, about 24 hours, but the result was a darkened skin with much browning/ blackening of banana underneath. I have since used it to make bait and will see how it does. I'm hoping that carefully keeping the temperatures lower will allow the rotting/ fermentation process to occur as it should. I have often used the hot car during the summer for this task and have had good results. It takes longer than constant heating, but usually within 2-3 days a banana that was in the car heat is ready.