I am having to do this because of a similar reason to above - one ticket for personal travel, and one a business. The personal travel can't be cancelled, because it's the last leg of an itinerary that is not refundable, with other people travelling on the booking, and the PNR can't be split because it's partially flown.

I can't quite figure out if one of the tickets will be a no-show, or both will be given boarding passes and two seats for extra space, but only one BP is swiped to enter the plane.