DS has recently started to boycott veggies, too. He used to love almost all of them, but I think he learned to be picky at the day care - they serve everything, but if you eat all your favorites, you get more of your favorites (for ds, this is fruit and meats). I have done the grating and hiding thing, too. We have a VitaMix (really powerful blender) that disguises any veggie any way I want.
Just a new trick I tried...He didn't like the dried veggies, either, but I bought some freeze-dried corn and tomatoes and peas and he loves them! They were a little pricy, but I am sure it's temporary, since daddy and mommy both love their veggies!