For me, may it be Sphagnum moss, peat moss or coco peat. I make it a point to soak the medium in water for at least half day to make sure they have absorbed water. Do not worry too much about rot because after using them to pot, then you can start regulating the water. But frankly I'd be more concerned about drying up than rot (in my case only) I have killed some small Neps from lack of water than too much watering.
Please note that cocopeat or cocochips act the same way as dried LFSM they cannot absorb water easily if dried up.
In your case, as suggested by fellow members, dunk the whole thing in water till you see darkening of color and you know they have absorbed water, the water will drain quickly anyway and then just water as often as you want.
you didn't mention what species of nep you are keeping, because as we found out while we are updating the nepenthes care sheet database, some nepenthes want wet roots and some can take or likes drier or airier medium.
TTFN
Arvin