Pretty much the tape is the easiest way. I usually put tape on the backside of the button holes and then body fill right over them. Then remove the tape while the body filler is still wet and use a toothpick or q tip to push the excess thru the hole and clean up the edges as much as possible. Then once its dry sand down smooth and spend that extra 20 min. "fine" sanding around the holes. Usually a peice of sandpaper wrapped around a pencil will let you get the inside edges of the holes pretty good.