To answer my own question: It can't easily be done. Two options: Create a boot microsd from the eflasher images, boot that, use the eflasher program to write the emmc Use a typec image with the Linux_Upgrade_Tool to write the emmc using instructions from the wiki Untested, but I think once the above...

I have the microSD to eMMC adapter. I've tried flashing the Friendly Desktop sd and eflasher .img files using dd. In both cases, the M4 will boot from the eMMC (green LED blinks), but I get no desktop video. HDMI is putting out a signal of some kind, but my Dell 1080 monitor shows only a blank scree...

The eMMC module can be plugged in two different ways rotated 180 degrees. Should it hang toward the hdmi connector or the audio connector?