Friendlyarm people need to answer the direct question (for Raspberry Pis the answer is that only the new Pi3 is able to boot from USB drive, no other Pi).
I once used "plop" boot manager for USB boot without BIOS support (UHCI, OHCI and EHCI) on an old laptop with dead harddisk (plop was booted from CD):
https://www.plop.at/en/bootmanagers.htmlIt is free software and can be compiled, so maybe it can be used with H3 based Neo/M1. If that is possible, then plop would be booted (very quickly since small) from an SD card and continue booting from USB drive you have configured.