it's not just an belgian adress, you need a belgian bank account number as well !
I'm allready registered, so I can't help. You'll have to find someone in Belgium who's willing to let you use his address and who'll pay the subscription fees for you - or sue the dealer.
I'd try my luck on a dutch satellite forum (like sat4all.com), you'll find a lot of Belgians there, but then again, being a satellite forum, most of them will allready have a TV Vlaanderen subscription.....