You could always do the old "leave the keycard in the room and just walk out" trick - they won't go in and collect it until after the checkout time for the 2nd night. It mildly inconveniences the hotel, but would ensure you get 2 nights logged.

I did a variant of this at a Holiday Inn a couple of years back, when I checked in due to the only road to where I live being closed by a power pole coming down. Checked in at 4PM, but by 7PM the road was back open - so I headed home. I then returned the keycard the following morning (dropping it off on my way into work), which caused all sorts of confusion. In retrospect, I'd have been better off just leaving the keycard in the room and not saying anything! I did, however, get a night posted. If I'd checked out at 7PM they would have charged me, apparently, but not credited the night - as you have to be there when they do their overnight run for it to count.