As others have said, the big question here is whether or not you can PC Exec->Prestige.

For your time crunch - I'd guess that you could utilize the airline credits, let your AF post, and wait for the credits to hit. After that, call in to cancel and get a refund/rebate on the AF. You may not get the full $450, but I believe you have up to 90 days. I may be confusing the policy with Chase or Amex, though.