Not so sure. I have done that too successfully last year for the Labor day weekend. Here is what I did:
1. Made 2 seperate reservations one for me (Thu-Fri) and one for Mrs. crazyhorse (Sat-Sun)
2. Sat morning, Mrs Crazyhorse goes down to reception and checks in.
3. We transfer the bags to the new room
4. I go down and check out of the old room.

As usual, the free night cost wasnt taken off and I had to remind the front desk to take it off. Also combined this offer with an offer for a $25 gift card for a weekend stay that was running and so we ended up with 2 x $25 gift cards as well. Paid the amount of the bill using Marriott Gift Cards from the 10% off promo and ended up saving more there too.

All in all a very cheap stay for 4 nights. (Approx $60/night)