Unable to update EFI (BIOS) using nsh script when A/B partitioning is enabled

Question

I have embedded linux (Buildroot based) OS with A/B partitioning enabled and trying to install EFI upgrades using nsh script. Note: Using EFIStub (directly booting kernel from EFI)

Here is the startup.nsh script, I wrote:

@echo -off
mode 80 25

$1:
if exist .\AfuEfi*.efi then
 echo "AfuEfix64.efi found!"
 if exist D015000U110XI12.BIN then
  echo "updating firmware"
  AfuEfix64.efi D015000U110XI12.BIN /p /b /n /x /me
  rm AfuEfix64.efi
  reset
 endif
endif

\\efi\\boot\\bootx64.efi

To me logically this could be done through following sequence:

1. Booting through UEFI shell
2. Determine the correct partition is selected (i.e. FS0: or FS1:)
3. Run fs0:\startup.nsh fs0 (if FS0 is the highest in boot order else FS1)

I would like to perform above all steps without manual intervention.

For Point 1, I think I can alter the boot sequence in favour of efi shell by making changes in init script of initrd using efibootmgr. But, now I dont know I can proceed with step 2 or step 3 as the logic to determine bootorder in efi shell (e.g. bcfg) needs to be played on the efi shell, but how? Any idea?