In the past, people have the reported the ability to have an Aeroplan phone agent put an award itinerary on a brief hold, as long as you are able and willing to transfer your Amex points while you are still on the call. You would obviously have to have everything set up on your computer for the transfer before you called Aeroplan, so that all you would have to do is press one button when the Aeroplan agent holds the flights.

No idea if this is still an option.