Chocolate can, in very high amounts, but I don't think chocolate is a major part of Merc's diet. Wikipedia says "High dietary intake of animal protein, sodium, refined sugars, fructose and high fructose corn syrup, oxalate, grapefruit juice, and apple juice may increase the risk of kidney stone formation." I knew about the oxalate bit; it's the one usually blamed. Soft drinks containing phosphoric acid (typically colas) should be avoided.
Aggressive hydration is the easiest way to avoid more stones forming.