I could certainly get behind an idea that once you'd made it into the queue the race you selected was "held" for you for a limited time to prevent selling out during the check out process. There are a couple of other things that would need to go along with that, though.
First, you might need to eliminate or severely curtail the number of registrations one person could do simultaneously to prevent the early entrants from bogging down the system to get their whole group of friends registered.
Second, that approach can result in a different type of unfairness that I don't know how you'd prevent. Say enough runners in the system have the entire stock of Dopey bibs accounted for. When runners right after the get through, Dopey isn't available to them. Now say some of the first set don't complete their transactions on time and Dopey bibs are released back into the wild. You'll have a number of runners who "got there later" able to register for Dopey when earlier runners weren't able. Pretty much the same situation some are complaining about from this registration.
