You can hydrostatic drive the MGU-K from an engine ancillary. It's allowed in the rules, whether it's practical or useful is another story. Maybe you can harvest a tiny amount of electrical energy in the ES to make up the short fall from less MGU-K harvesting. Maybe drive it with differential hydraulic fluid, build an external pump and claim it's an engine ancillary, presto chango you have a way to drive the MGU-K which can not just charge the ES, but power the MGU-H as well. So in essence you can have both electric and hydraulic super charging, which means you can open the wastegate just that little bit more, which means more engine power.
The height of cultivation is really nothing special. It is merely simplicity; the ability to express the utmost with the minimum. Mr.Lee