Like others have said, by decressing the water to grain ratio a bit you can do it. I've done 14 pounds. Use the greenbay rackers calculator to figure out how much to squeeze in there.
Thank-you everybody for all of the replies, was at work so I just got to read them all now! I think I'll go with 1.1 quarts per pound, that wont be too thick (hopefully) and should leave me some wiggle room on top. At least I don't have to worry about a false bottom taking up any of my free space... maybe I'll take some pics on Friday and update.