Onion family plants are generally easy, peasy @Madetoshop. You may just be able to literally leave the sprout sitting out until you are able to plant it. I have stuck onion slices in the ground, put what is left of a scallion in a jar of water, and stuck all kinds of sprouts from the onion family in the ground, and all with good results. I did learn that half of an onion will not likely make another full bulb, however, you will likely get a lot of good green onion shoots to use in your cooking. A lot of the organic varieties do significantly better than the others, so you are already ahead of the game on that part. I'd probably just let it do its thing, and see what you get, which will likely be at least a little something, maybe enough of the green for a good salad or two. Rooting it indoors and then planting it outdoors sounds like a lot of work to me too. However, even if it doesn't work to plant it outside, going ahead and rooting it will likely give you some green onion shoots that you can use. I love the organic because they seem to do better on most all of the various replanting options than some of the others.
How many legs does a dog have if you call the tail a leg?
"Four. Calling a tail a leg doesn't make it a leg."
-- Abraham Lincoln