I have done something similar to this for a few years, but I do not "can". I put all my vegetable scraps in a freezer bag and when I have a couple of them, I put them in a crock pot with water, seasonings, etc, on low for as long as I can, strain it and put it in a freezer bag and freeze it. Then I use it when needed.
Thanks for posting this. I'm not faithful about saving all veggies but do save onion and celery and use them when I make chicken stock. You have inspired me to broaden my horizons a bit. I don't agree that this can be water-bath canned though. Vegetables are low-acid and need to be pressure canned. It would be best to just refrigerate or freeze the stock.If one really wants to can it, here is a step-by-step instructions. http://www.culinate.com/mix/dinner_guest/how_to_pressure_can_stock