keep some in a glass or vase in yr kitchen and just keep waterin. chop some up and fry em in neutral oil, provides a crispy topping and leaves you with some very useful oil (for salad dressing, sauces, etc). or just munch on em. or just look at them if you like
Buy some master blend water soluble fertilizer and you can actually feed those onions everything they need hydroponically instead of just letting them soak up water