My 7 year old Bassett Hound has had Cystine Stones removed from Bladder, resulting from extreme pain when passing excreter from back passage. He has been fed on Eukenuba from puppyhood. Our Vet thinks a Complete "Wet Diet" may help. What products similar to a complete type Eukenuba are available for effective treatment
Robert S Stacey (for Toby)

Sorry, I have not had personal experience with this but I did come across this information which sounded like exactly what you were looking for.

Diet Alteration: Diet alternation may be helpful as anything in the medical treatment of struvite, ammonium urate and cystine stones. Specially formulated diets can actually cause the stones - even large ones - to dissolve completely. These diets take time, often 60 to 150 days, to work. To take struvite and Hill's s/d diet as an example, the principle by which s/d works is that it contains lower than normal levels of large proteins, magnesium, and phosphorous. Less protein means less urea, and therefore, less ammonium and carbon dioxide formed by the action of urease. Remember that struvite is made up of magnesium and phosphate ions, so lower levels of these materials also decrease the quantity of crystals that can potentially be formed. Feeding s/d helps the urine become more acidic. And last but not least, Hill's has slightly increased the sodium chloride (normal table salt) to increase water consumption by the animal, thereby increasing a flushing action through the bladder and better keeping the crystals in solution.

NOTE: Do NOT use a urinary acidifier and s/d, c/d, or a similar diet at the same time.

However, s/d cannot be used indefinitely as a preventive because it is not considered a complete diet. Also, it is not recommended for use in patients suffering from heart failure or kidney disease because of its salt and protein levels. After the initial 60 to 150 day period, when medical therapy is actively attempting to dissolve the stones or sand that is present in the bladder, the animal is removed from s/d and placed on a maintenance diet such as Hill's c/d or w/d. Royal Canin, Purina, and some other companies have also developed specialized diets for use with dogs with urinary stones. If a dog is reluctant to eat one manufacturer's diet, it is advisable to try diets produced by another company.

Prior to the development of specialized diets, urinary acidifiers such as Vitamin C or dl-methionine were sometimes used to lower the pH of the urine in cases of struvite stones, for example. Specialty diets are now preferred since they alter not only the pH, but the concentration on stone-forming constituents. Remember: Do NOT give urinary acidifiers when you are using one of the specialty diets that also acidify urine.

Taken from:
Bladder Stones (Urinary Calculi) in Dogs