if you are thinking of doing this, maybe you should wait till january, its the slowest time of the year for single sales..

I guess as long as your spread the sales out across the country using proxies, vouchers should work..but then, they might notice something suspicious. one band sold (gave? not sure) sim cards with some credit on to fans to buy their single, and they got caught..

go upto people in the street, make them download by paying by sms (see 7digital.co.uk), and re-imburse them the cash. that way you arent using consecutive numbers, nothing is IP traceable, and its unlikely that they'll know..but it would take a lot of work..