It's true that you can't snap in the liners until you stop folding the diaper over, but you can still use them. Just lay them in the diaper, they don't shift or anything. The Sandy's liners aren't snap-in and they work the same.
It does depend on how big your baby is as to when you stop folding the diaper down but most newborns/small babies don't need the extra absorbancy of a liner. Most poop so often that they get changed way before needing more absorbancy. Only time you're likely to truly need a liner is when your baby stops pooping at night and you can then go longer between changes (ie to minimize nighttime disruptions). Then, depending how long we're talking about and how much of a heavy wetter the baby is, you may need a liner.