I got this issue resolved. The short answer is that Microsoft provides zero ways to do this with Windows 10 alone. You can only do it using a custom non-Microsoft boot loader. However, you risk future breakage going this route, because Microsoft is rather reckless with future change.
It turns out that my own hardware has support for this in BIOS mode. I simply wiped the large single partition and created three virtual partitions:
*2048G BOOT
*2048G DATA
*14XXG TEMP

I reinstalled the latest Windows 10 via BIOS boot. It's RAID10 cached, so performance is still fast.