I don't know anything about it being banned but you never know.. Maybe pop into RipCurl at the Torquay shop and ask them..
About eight years ago we took our 17' long down wind boards out at Bells and paddled back to Torquay on a pretty flat day and got away with it but on a day when there is good surf I wouldn't recommend it unless you are well a know local.. Although it's do'able in my opinion it's a bit NQR and you could be asking for trouble with the locals both on the water and off..
Unless it's a big deal for you to you to be able to say "I sup'ed Bells" I'd recommend that you take a five minute drive to the south and go out at Point Roadknight or drive five minutes north and go out at Point Danger at Torquay..