Apologies if this has been mentioned before, but: I wonder why ATA don't offer an option to "buy now, but ship at the end of the sale", such that people can add items to the order through the lifetime of the sale. Saves on postage, better for the environment (as opposed to multiple smaller parcels), and gives their more dedicated customers the ability to buy without fear of items selling out.
I can't imagine it would be terribly difficult to implement, though I'm sure it's a limitation with their third party payment page - the same one that won't let you use a discount code if part of the order is BOGOF.
(Though, now I type that, that's another problem that it would solve. Put in an order for regular items, use the code. Put in a second BOGOF order, and then just choose to link it to the original order.)