Thanks for the ideas.

Reusing a portion for seed is a given. I have several heritage varieties and seed has never been commercially available (the skins are too delicate for commercial potato production ... or maybe they have something against flavour).

Don't need 500 plants though. (And somebody would have to hill them!)

The vodka idea is interesting. I thought of that before and talked to a skilled winemaker. There would still be a lot of waste, since yeast doesn't eat complex carbohydrates. (It's also a lot more fuss than juicing my surplus apples and raspberries for wine.) Unlicensed distilling is illegal here, although they won't go looking for you unless you start selling it.