if a traffic warden walks past, he WILL ticket the car.
in town near me theres a residential area where people park, i've seen cars parked slightly over the dropped curb so they are blocking a drive.. all with tickets on. (and those that are slightly over part of a yellow line havent been ticketed..)
its an obstruction.. like if you park on the pavement, or half on half off it.
maybe phone your local police station\traffic dept up direct and advise them, take a couple of photos on the car on your mobile or something as proof.. (note the reg of the car and how many times it happens a week!) depending on where you live i'm sure there will be someone official on hand to note the reg down and tell the driver off if nothing else :)