Yep, good idea , we have suggested it to WGT.
Their initial response was "we dont want to make the decision on whoich ball you have in your bag is loaded up next"
We suggested we could nominate balls in our bag as being 1st/ 2nd/ 3rd/ 4th back up etc
or, a pop up like the one to 'purchase more' when you are running out, to offer a selection from our bag.
But, you see, WGT would prefer it if the pop up forced us to buy more balls of the same type, rather than use up the litter of single balls we have in our bag that we have already PAID FOR.