some sort of time-delayed one-per-bottle campden tablet would be a neat idea I think. You could prime your beverage, toss in a tablet, and cap the bottle. Yeast would have some time to carbonate the brew, then the campden kicks in and kills them.
does anything like this exist? I would use it to make some rootbeer for my son (he's eager to brew some beer with me that he can drink, too.)