If you cook the berries to make preserves, pancake syrup, or wine, the poison will be neutralized. The toxin is a cyanogenic glycoside known as sambunigrin. Letting the fruit completely ripen helps to reduce the toxin, but cooking the fruit gets rid of it.
Elder-flower fritters taste great! I prefer whole-grain pancake mix with lots of cinnamon. Remove the flowers from the stem, and while cradling them in a ladle, dip them in the batter and drop into a shallow puddle of oil in a hot skillet, and fry till golden brown on both sides.
To get enough Elberberries for wine production, this is the time of year to take greenwood cuttings from mature plants. They root quickly in a vase with water, then pot them up and allow them to double in height with foliage, and plant them out.