Most artificial sweeteners (aspartame, sucralose, etc) pass straight through the body into urine! So, for sweet-tasting pee, just consume some of these!
Unfortunately, both aspartame and sucralose give him headaches, and so we avoid them entirely. But luckily, Stevia (natural non-sugar sweetener) works the same way! The right amount, combined with a decent diet, will make one's pee taste downright craveable!
Meats and milk products (milk, cheese, etc) will make the pee more acidic and therefore more bitter and less palatable, IME, and so should be consumed only in moderation. Mode