Rescue modes when booting from external drive?

Docs at https://doc.turris.cz/doc/en/howto/omnia_booting_from_external_storage say that once I boot from an external device, rescue modes probably won’t work. I can confirm they don’t.

Is there a way to enable them again? E.g. manually changing some scripts, some u-boot flags or whatever?

As my eMMC is dead, I’m forced to boot from an external drive, but the rescue modes thingy was really helpful and I don’t want to say goodbye to it.

Hazarding a guess - the button scripts are probably embedded in the omnia-initramfs-zimage that resides in one of the NOR-SPI flash partitions (probably /dev/mtd1)