Today through April 30, Gap is running a Facebook promotion to get shoppers into their physical stores, without even giving anything away.

The retailer is advertising “winning the Gap Royal Treatment” (seems like no corner of retail has escaped the Royal Wedding) as a Facebook event, but in order to enter the sweepstakes, you have to visit a Gap store and scan a designated QR code at a specified outpost.  The big prize is use of their “employee discount”– 50% off — for a year.  They’ll pick one winner per store.

Though we’ve been wondering how much QR codes will make in-roads in the world of commerce, it’s notable that Gap is relying on them heavily for this promotion — basically you’re shutting out any shopper who doesn’t have a smartphone.  It seems like giving out a numerical code unique to each store would have been an equally efficient means for entry.

Other than this hitch, though, it’s a very smart sweepstakes — besides luring people into actual stores in order to enter (a dilemma that a number of shop owners are grappling with these days), Gap has also pretty much ensured that the winners will wind up shopping there.