Just an update...
With the cider I'm using (28.2g of sugar per 8oz, yum) I figured I need to add about 0.18 gallons (0.68L) of cider using mrfocus' method, so 1/2 gallon is much too much.. Going to bottle tonight, so I'll let you know how it tastes in a couple of weeks :)
Also, our first-ever...