Depends how much prune - Duncan Incapable's gluten-free ersatz-ale recipes use it, but you get very little per pint so the well-known effects don't arrive.
Blueberry is a great adjunct in TC, so should work well in a wine. And banana is good for body. I think it sounds like a good idea.
Recipes I've seen using bananas say to let them get really overripe before using. And probably not too much banana - it's a very distinctive flavour. There's gonna be pulp.
CJJB suggests 4lb nanas + 1/2lb skins for a gallon, with grape concentrate, a lot of sugar, and some acids. And amylase...
Say, half that amount of nanas, 1 or 2 litres blueberry juice, raisins instead of concentrate, not too much acid as the juice will have some, calc the sugars and add enough to get the ABV you want, should be good.
