We never fixed it when they came out a little runny. We would just use them as "flavored" syrups for pancakes, french toast and waffles. I didn't think you could fix them either. Thanks for sharing the link Brewjen.
I never realized that you could fix runny jelly, so that's good to know, although I doubt I'll ever do it. To me, it's a lot easier to just use the jelly in other ways (in smoothies, over ice cream, etc.) than it is to do all the work. If I ever make a batch that fails to set properly, though, I'll have the solution on hand now.