I have done this many times and in many jurisdiction you need to enter the persons name who actually stays in the room into the fd system, however I always make a point to at checkout requesting two invoices one for each room which I then pay for one by one. At least from me this have never been a problem. Alternatively you could put the charges of the second room onto the bill of your room, this have glitched a few times but after emailing scanned bills to spg it always worked out in the end