I can't find it. I find people talking about doing it, but not with numbers. Different concentrations of sugar from one brand/variety of juice might be an issue now than I really use my brain on it. It might just come down to having to read the nutritional label for sugar content and figuring out how much sugar there is per ounce of juice and formulating it from that. As many times as I've heard people suggest priming with juice so that you're adding more apple instead of just more sugar, maybe priming with sugar is just plain easier in the end. If anyone on here has primed with juice, I'd just love to hear about how they did it and how much of what they used.
On a related note, I'm thinking about picking up some fructose to use instead of the dextrose in my batch. Mainly because I can pick up fructose granules on the way home from the radio station today instead of running down to Homebrew Heaven after my day job on tuesday. From what I hear, it should work just the same. I've found the co-op up here has tons of great stuff I can use. Gotta love them hippies and their products.