All the reading I have done on kidney issues show me that struvite stones are produced due to an alkaline urine and oxalate stones produced due to an acidic urine. What is the pH of your dog's urine? Struvite stones are produced because the dog either has a naturally alkaline urine which is rare or a UTI. Oxalate stones are formed because of a defect in the dog's metabolism and if the urine can be made less acid the stones will not precipitate out. There are also cystine and urate stones that form due to a defect in the metabolism, I don't know if pH is important in those. Here is an article about struvites with links to articles on the other kinds. Your vet should have a clue as to what sort of stone it might or might not be, struvites are the only ones that there is agreement about the possibility of dissolving.
http://www.dogaware.com/articles/wdjstruvites.html
Sounds like you are planning on using the canned stuff? There are many brands of this type of food, it is remotely possible your dog would consider one sort tastier than others. Since the prescription food depends on a delicate balance between the minerals found within I wouldn't mess with any sort of treat or addition to the stuff. You can slice the canned and bake it for a treat, perhaps that might work. You could mash it up and make a gruel with water if your tap water is suitable.
http://www.dogaware.com/articles/wdjstruvites.html
Sounds like you are planning on using the canned stuff? There are many brands of this type of food, it is remotely possible your dog would consider one sort tastier than others. Since the prescription food depends on a delicate balance between the minerals found within I wouldn't mess with any sort of treat or addition to the stuff. You can slice the canned and bake it for a treat, perhaps that might work. You could mash it up and make a gruel with water if your tap water is suitable.