I don't do a purely pelletless diet but my girl who had a bladder stone and her sister are on a very limited pellet diet. They each get 6-8 KMS pellets a day, I just feed them to them like a treat and they love it.
The key is a variety so they get all their ncessary vitamins and minerals. Leaf lettuce, peppers for vitamin C, tomato, cucumber or zucchini, radicchio, belgian endive and escarole are all good options.
Your pigs are young so they may not need it but a small vitamin C and multi vitamin supplement wouldn't hurt. I use the oasis multi vitamin drops. I don't put them in their water though, I either dilute a couple drops with a bit of water and syringe it to them or I soak a pellet in a couple drops and feed it to them. They get this 3 times a week.