I'd save the miles and use SWU's at the airport. It would be the only way to go if you are on a highly discounted Y fare, since u/g with miles requires that you be ticketed on certain Y fare types, which may put you you already, depending on the type of fare you purchased. Also, you may even have a chance at a double u/g, SWU to J from Y, and then possibly an ops u/g to F at the gate if the flight is full. As a 1K with UA, especially out of ORD, there may be no limit as to what might happen. Congrats on your 1K status!