I'd just supply your flight information in the reservation. As long as your flight isn't delayed arrival by more then a few hours, there won't be really any issues in terms of your car still being in a stall assigned to you (in a Gold Canopy location) or your documents pre-printed in a Gold Counter location.

I usually make my reservations for 15 minutes after my scheduled arrival, giving me time to collect my luggage as well as any possible delays (although lately, I've actually been arriving early).