I need an additional 7,000 PQM and am not interested in a mileage run. I was hoping to purchase a ticket, buy the miles with Premier Accelerator, and cancel the ticket within 24 hours. I assume this strategy will work, that even though I cancel the ticket I keep the purchased PQM?

I already have one purchased itinerary, Dulles to London, but the "additional miles" for sale are 20,000 or 30,000. I'm not interested in buying that many extra miles when I only need 7000.

I can't see how many additional miles will be available for purchase until after purchasing a ticket. Thus, any strategies out there to help me select the best ticket to purchase that will offer me the needed 7000 extra PQM for purchase at the least cost? Thanks!