Wouldn't a,false address be logged when you went to pay though? Obviously that creates its own challenges of having 6 people ready with 450quid but a lot of sites (well definitely ticketmaster on some sales and some other random ticket sites ) insist on same address for booking and payment.
Logging in with reg number obviously helps but creating multiple registrations using different addresses is really easy I am afraid. Fake ID's are all too easy to get hold of.