I agree with you that using Coca-Cola and asparagus sounds a little over the top, but the principle of first using a strong acid to dissolve the kidney stones followed by using a good diuretic and then flushing your kidneys with lots of distilled water makes good sense to me.
I think the active ingredient in the coke is phosphoric acid and I suspect he hope is that the asparagus will act as a diuretic..
I would assume that (ortho)phospphoric acid it should work but Why drink coke!!! all that Sugar & caffeine etc...why not just buy orthophosphoric acid from the health food store...
orthophosphoric acid is available und brand names like as "Phosfood Liquid" and "Super Phos 30".
There are many good diuretic herbs & teas out there. Watermelon seed, cellery seed, & parseley seed teas, are available as well as a multitude of other kidney cleansing tea blends.