Bug#609722: is still there
you're right: If the rest of the installation works well with netboot
from USB-Stick, grub-install should do his job, too.
And this image should *then* be a valid alternative.
But I am unsure, if that can be fixed before the release so it's perhaps
something for the errata - state that netboot can't be used on usb sticks.
Ben Armstrong said, the mini.iso is not suitable:
(and follow-ups) so please use a netinst.iso
To test the installer from a usb-Stick I used
hd-media/boot.img.gz (yes you can also use initrd.gz and linux
separately) together with the ISO
Or you could try the hybrid CD alternative and dd the netinst.iso
directly to the stick.
By the way: You can find the new installation manual at:
In my eyes the documentation concerning USB-Installs is still very
confusing or even inconsistent!