The same way that One Direction do.
This has tickled a vague memory in the back of my mind about a legal case brought against one of the endless stream of manufactured pop bands. If memory serves, a disgruntled punter was miffed to discover that the show she'd been to see wasn't the "artists" singing live, but was actually the "artists" miming to a pre-recorded track, so she sued. And if really rusty memory serves, the courts found for the pop group - the advert of the "artists" singing didn't actually imply that they would be singing.