Does the reservation have to be prepaid? That could be troublesome as I've had some hotels deny me a receipt on a prepaid reservation because it had a zero balance and there was no proof I had paid for the reservation! I remember pointing out to the FDA that the reservation was in my name, I was standing in front of him with the credit card I used and my ID and he still wouldn't give me a receipt.

If possible, make a non-prepaid reservation under partner's name since they are Plat. Have them put you down as the second guest. You arrive 1 day earlier. The hotel may or may not grant benefits for the first day until your partner arrives (most likely will). At check-out, since you are paying the bill, ask them to change the invoice to your name. I know they can't do this with a points reservation, but should be doable with a cash rate. Pre-paid is a wild card.