Install With New EdgeOS TFTP Recovery Boot Loader

Has anyone successfully installed OpenWrt on an Edgerouter X that has the new (as of v 2.0.4) Ubiquiti bootloader installed on it? I've hooked up a USB serial adapter to the serial pins, fired up PuTTY at 57600 baud and tried to hold down the "1" key while it powers up, but nothing happens - no bootloader menu comes up in the PuTTY screen from which to flash OpenWrt.

I can flash the Ubiquiti recovery image over eth0 if I put it in TFTP mode (reset for ~30s until solid lights, release, wait for sequential blink through, then put the recovery image to host 192.168.1.20), but the bootloader only accepts Ubiquiti signed images in this TFTP recovery mode- it rejects the OpenWrt binary.

And a reminder (embarrassing for me - it took me a week and I needed to get help on the Ubiquiti forum!) if you do this: don't forget the Edgerouter does not come up with a DHCP server running on eth0 by default. You need to manually set your workstation to 192.168.1.x in order to reach the router on 192.168.1.1.