Call the hotel reservation manager and see if they help you out. If the third person is child >12 yrs old then may be willing to work with you but if the third person is an adult. Then they probably will not move.

I had to do this with LM in Hong Kong. I have three kids and hotel T&C's stated no more than 2 people per room. I booked two rooms and SPG would not accept my reservation as I had 5 pax's total so one room would have be over their capacity. Discussed it directly with LM reservations and they didn't make an issue of it.