We have done this several times. We just go to the regular Boardwalk parking lot and tell the attendant that we're there to shop/eat, or whatever. They have usually just waved us through and said to have a good time, but we always go at non-peak times when there is plenty of space in the lot. I think the standard is that there is supposed to be a three hour limit for non-guest parking, so you may be told this. I'm not sure how they enforce it. There is also a parking lot directly across the road and behind the Hess station from the Boardwalk parking lot which is open to anyone and doesn't have an attendant.