if you can get the license number on camera, can you visit the parents and tell them you'll report it to the police if it doesn't stop? if they don't know what their kid is doing, that might do it.
if not you can run an ad in the local paper and embarrass the heck out of the whole familiy.
what i can't understand is why the police and/or the post office is unwilling to step up to the plate. unless it's their kids. i'd be going to the att'y general, the postal dep't or whatever it is. there has to be a gov't office for this. look in the phone book or google it.
when i called the police at the beach house, they cracked down and found the kids, would you believe on bikes? morons!