Thanks for your comments.
I encountered some comments regarding this issue
in the past that this is doable through some combination
of "chainloader +1" GRUB commands.
After all, Windows is another, sort of, boot loader that
is invoked through some GRUB commands combination
with "chainloader +1" when it coexists in a system with
Linux distros and is invoked from this other distro.
This was basically the essential idea from the past comment,
so I was just curious if anybody has managed to work out