I scatter feed my pellets, too; about 1 tablespoon per piggy per day. It minimises food bullying and provides extra enrichment activity that stimulates foraging behaviours.
We have had a closer look at the calcium content of pellets and even the no added calcium ones have weight for weight more calcium than the vet highest in it, kale. Reducing the amount of pellets gives you more leeway for your veg diet. They will get their vitamin C either way. Pellets and veg together replace the supplementary role that wild forage used to play in the mainly grass/hay based diet guinea pigs have evolved on.