Make them a slurry of their normal feed with water & unsweetened yogurt, wouldn't hurt to drop a couple of raisins in there to pique interest. Normal feed for balanced diet, yogurt will offer probiotics even though they don't digest dairy well (they'll get runny poop, but they've already got that from the disease & from the meds for the disease, so what's a little more, right?) and raisins for straight up calories and they taste good.
