How long do you want to make it? Supposedly dextrose is a precursor of of isoamyl acetate and higher levels of it in your wort can boost banana. If you're decocting you can boost dextrose by holding your decoction at alpha rest temps to create dextrins, then using that to raise your main mash to a limit dextrinase rest at 140F.
FWIW, I added corn sugar to my last hefe at the end of the boil after hearing this. I think I got a bit more banana than usual, but it's far from conclusive.
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