Ideally, I want to keep all the buildings doing something all year, and I hope to be able to just leave the buildings on repeat and have the dwarves do their thing, but I end up with lots of Rum and no syrup, or some other non-ideal situation when I do that.
There's no ideal solution, but there are a couple of things you can try in order to minimise the problem.
1. Small stock of sweet pods right next to the mills and well away from any other freely accessible millables. The first thing milled will be something fairly random, but after that the dwarf should go straight for the sweet pods. You'll need to do this every time you want some sugar, but it can be set up by the manager and then forgotten about.
2. Get your sugar from the caravans. You won't get much, but there's no messing around. Mill products from trading always come in bags of 10, which might or might not be useful to you.
3. Set up a sweet pod only stockpile around the brewing area so that the sweet pods are closest to the stills, and restrict and unrestrict the brewing of sweet pods as necessary.