Malic acid that is found in fresh unpasteurized apple juice, and orthophosphoric acid both help to break down stones prior to flushing. Phosphoric acid is found in Classic Coke...hence the Classic Coke flush, although there are better ways of ingesting orthophosphoric acid. If you click on the liver/gallbladder flush recipes you will see instructions for a flush that uses orthophosphoric acid. I've done this flush with great results.
There are also some Chinese herbs that help to break down stones...others will have to provide more info on them.