Consider an exemption up to a certain level like they do in Australia, otherwise this would be disastrous for small businesses. They already deal with an unproportionate burden of compliance costs. Given that small businesses return far more benefit to the local economy than do multinationals it make little sense to load more costs onto them.
Minimum pricing might be more effective as tool to reduce binge drinking, and supermarket sales should be looked at too, but just increasing excise tax risks dampening the craft end of the beer and wine markets. It's the small producers that are driving a positive mindset change in Kiwi's towards quality over quantity, so to punish them would seem counter-productive to the goal of your policy. (I should disclose that I work in the wine industry so I've got a COI in this area, but it also means that I know a bit about it.)
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