Well, trivially (and not ideally) we’d work around this by not doing it. i.e. only placing items to which these rules might apply on an order. Oh no, now I have to do a separate order / invoice / delivery paperwork for those half dozen cans.
But all we’re really doing with that is saying that cans shouldn’t be considered in the calculation. So what we need to do is look at an order, see what discounts are applicable on this order - and apply them only to the eligible lines.
Have done a FR: Better price book / discount rules - Ideas & feature requests - Breww Community