I think you could go by with feeding them less, as trying to force feed them will lead to a quick decline in water quality. I used to feed mine to the point in which their bellies looked bloated, but the water would foul too quickly. Now I feed them much less, just mere morsels to satisfy their appetite- a quick snack here and there. Since they're just floating in the water they're not expending much energy anyways, so one doesn't have to feed them so much. Long story short, I became too lazy to change water often, so I stopped the high quantity feeds. I'm sure feeding until bloated would be the quickest way to grow them out though, but would require subsequent water changes.