You may want to look into "stepping up the yeast starter" that invloves making a starter, let if ferment out and settle down, decant the spent wort and boil and cool more malt extract (or whatever you make your starters from) and ferment again on top of the yeast you just made/cultured (or something like that). This method is great for using in lagers or when a large amount of yeast is needed in a higher gravity ale. That way you are not pitching all the liquid used to create that large amount of yeast. I've heard of people doing this 3 or 4 times to get the amount of yeast they need though i've never done more that 2. Bad brew, most of the gallon jars that you can buy are not flat around the edges so a spinner bar usually does not work, ive tried on all mine-fyi.