That's really neat - love your thinking, keep a bit of K, P and Ca going in - plus bonus to outdoor growers apparently its really good for aphid deterrence. We have 6 banana trees next to the house so I'm sending my wife scrumping over there in a month or so when we need to start thinking about flushing."final flush" I make a banana peel tea that will be the only feed added to the water until finish.
My thinking on the 'final flush' is more about removing nitrogen at the end of the grow to induce colors, while still providing some food for the flowers to continue ripening than to somehow wash leftover salts out of the cells of the plant.
Nick