Have you considered modifying the order process to place items on "hold" while the customer continues to
shop? I can't see a 10 minute hold hurting anyone or the inventory count. Lots of sites do just that and it seems to be very successful.
I planned to purchase 3 50ml bottles but ended up with only one 30ml bottle because they kept getting yanked by someone else though I placed them in my cart first. Fair or not, it's frustrating no matter how you look at it.
With a product hold system in place you still wouldn't end up with backorders. If a customer didn't check out within 10 minutes of cart activity the product would go back into the stock count.
Just a suggestion to relieve some customer frustration. My point is: give your customers a little time to
shop 
As it is, we'd have to check out after choosing every item to avoid losing an item. We'd be racking up some hefty shipping charges on those individual orders.