The usual thing to do here is to rsync the image file from your remote build machine (if it's volteer-borealis and you're building in ~/chromiumos, the image file is ~/chromiumos/src/build/images/volteer-borealis/latest/chromiumos_test_image.bin) down to your Mac, then use the Chromebook Recovery Utility extension
to write it to a USB flash drive (click the settings icon and "Use local image" rather than telling it your model number), then proceed with the USB flash instructions (put device in developer mode, ctrl-F2, root, enable_dev_usb_boot, reboot, boot from external drive, log in as root/test0000, chromeos-install). After that, you'll have SSH access, and you can use a reverse tunnel to make `cros flash` work for future updates.
I'm not aware of any way to do the initial push over SSH, as developer mode by itself (i.e. with a normal CrOS image, not a test image) doesn't seem to have SSH set up. If anyone here has a link to info on how to do that, I'd be very interested too!