I never tried getting the green hulls off before they were "soft". My grandpa had large gravel in his driveway and would lay out the nuts in the tire path and run the car over them, then us kids would pick out the hulled nuts. Gets your hands stained if you aren't careful...and maybe if you are careful.
If you wait until the hulls are soft, you can sort of roll them under your boot and pick out the nut that way. One year I made stain for my brother who is a wood worker. Don't know if he used it or not.