This is an old trick, but udev added a little complexity, so let’s give it a try. First boot on a Ubunty CD, open a console and run:

(here my linux partition is sda2, second partition on a sata disk)

mkdir /media/mnt
mount /dev/sda2 /media/mnt/
mount -o bind /dev/ /media/mnt/dev
chroot /media/mnt

=> now you are on the destination disk, so you can install grub.
grub-install /dev/sda

Of course you can do a lot more stuff, like changing fstab etc etc .. but the trick is to mount + mount bind + chroot