This allows booting by specifying the boot device rather than the bootloader specifically in firmware configuration.
In /opt/vyatta/sbin/install-postinst-new change line 148 from:
output=$(grub-install --no-floppy --recheck --target=x86_64-efi --root-directory=$grub_root --efi-directory=$grub_root/boot/efi --bootloader-id="$bootloader_name" 2>&1)
to:
output=$(grub-install --no-floppy --recheck --target=x86_64-efi --root-directory=$grub_root --efi-directory=$grub_root/boot/efi --force-extra-removable --bootloader-id="$bootloader_name" 2>&1)