How searching for EFI-directory with custom-bootloader grubx64.efi?

[Dernsen]

I created my own signed custom grubx64.efi with grub-mkimage for
secure-boot enabled system. The grubx64.efi points to a grub.cfg file
within same directory as grubx64.efi, this grub.cfg points to the
grub.cfg file on the /boot, which starts the system. This works all
pretty fine.

The grubx64.efi is signed, so you can not edit it after signing and so
it is a custom bootimage, this should work for installing on any
amd64-efi system. So I set within grubx64.efi:

set root='hd0,gpt1'

set prefix=($root)'/EFI/linux'

configfile $prefix/grub.cfg

Usually EFI-directory is 'hd0,gpt1', if its on second partition
'hd0,gpt2' my setting will not work anymore. Searching for uuid or label
will not work, because these are different on every system, too.

How could grub search specificly for the EFI-directory , which has to be
on every EFI-system?