Just wanted to add a data point in case others, as I have, find this thread looking for answers.

The HKG mar riot was totally booked for a saturday night stay. However I noticed that if I put in both Saturday and Sunday it would give me a room.

I called Marriot and they said since you are a gold member I should call and ask for the frond desk manager (NOT reservations) and see if they will chop it in two.

I called and the woman told me to book the two night stay, which i did while she was on the line, and then giver her the confirmation number. In about 30 seconds she was able to change it to a one nigh stay. I refreshed my screen and my reservation was exactly what I had been looking for.

Not sure if this will work for everyone but it CAN happen and it is worth a shot.