Seasonic officially calls the new connector the "Nvidia 12-pin PCIe Molex Micro-Fit 3.0 Connector", which suggests this is the very same proprietary connector designated for the next-generation ...

A 12" or so long female-female 4-pin Molex cable would seem to solve my problem (minus powering the floppy and CD, which is less critical). It would be even better if I could y-cable off of it to ...