Another way to rehydrate over dry herb is what smokers of fine cigars do if they become over dry. Take a new, or absolutely totally clean sponge, moisten it and then squeeze out as much moisture as possible and add it. In the case of while curing in jars you would cut a small square of sponge for each jar or you could temporarily put it all into large ZipLoc bags and use an entire sponge or half of one.
A brand new never used sponge is best because it will not have any bacteria or odors. If someone does not have one handy and doesn't want to purchase one they can run one they have used through a clothes washing machine, hopefully with unscented soap and if not with a minimal amount of soap and then rinse the heck out of it, and then use it.