A reader was wondering how to make fruit leather for her child who was allergic to the citrus in the commercial products. I came across a recipe this morning, so here is the link to the original post. To replace the citrus, use either a light vinegar (like champagne, or white balsamic), verjus (sour grape juice), or perhaps a little powdered ascorbic acid (Vitamin C, which you can find at Whole Foods and other health food stores). Perhaps tamarind -- which you can find at Latino or Indian stores.
The best tip seems to be to have a neighbor with a full-to-bursting fruit tree of some sort for a constant supply. :)