So, re-applied kaolin (which I hadn't in quite a while and there has been a lot of rain). The rain will come back on Wednesday, but for now at least hopefully this is something...
Here's an article about kaolin on aphids (though not specifically cucumber aphids): https://www.semanticscholar.org/paper/Effect-of-Kaolin-Particle-Film-Formulation-Against-Alavo-Abagli/20f7c744e281f36324d1601aa32aa3a8282e9329