I was telling one of my friends how I make cider from storebought juice, and how I backsweeten with concentrate, and why you can't really do that in the bottle, etc, and we got to talking. Here's the idea:
Start with a 5gal carboy with 3 gallons of treetop juice (est OG 1.050). Pitch a healthy dose of ale yeast with some nutrient, and allow that to ferment mostly to completion. Add 12oz of treetop juice concentrate (est OG 1.200-1.225). Allow this to ferment, and repeat. If a total of sixteen 12oz containers of concentrate are added, this will net 4.5gal of cider with an effective OG of 1.100-1.108 with the help of no sugar other than that which came from an apple.
Perhaps I should try this once with 1 gallon of juice and 5 cans of concentrate.