I've done the hack with Ryobi but not Milwaukee, but I think the procedure is the same.
When you add all of the items to your cart, there will be 2 lines on the receipt. One is for the tool+battery combo, and the other is for the "free" battery.
Select in-store pickup for both items. Then, for the item you don't want, change the pickup store to a different location that you will not pick up from. After 7 days, the pickup will automatically cancel. Or, you can pick up the unwanted item and return it immediately. The key is that the pickup stores *must* be different locations.
I ordered the sawzall, grinder, and 6.5" saw. Not 100% sure that I'm going to actually go through with the purchase as I'm already on FIVE battery platforms (including OPE). Should I really add a sixth?