I think most hotels would be willing to save you the hassle of physically removing all of your bags and belongings if you simply found a reasonable soul at the front desk and explained the situation.

"Mrs. Sbtinme and I are here for 2 nights, but since we each have SPG accounts, we are both looking to earn points for one night (each) for this stay. Could you see to it that we don't need to check out." I would think that most every front desk manager would quickly agree and just process the paperwork to close out the first night's stay.