Some caveats - a) I've never done exactly this so I can't promise it will work b) I strongly question the wisdom of running Trisquel on a machine too small to run the text mode installer.
Having said those the procedure will be something like boot text mode install get past select language and keyboard Ctrl-Alt-F2 to get to the second console Press Enter to start the Busybox shell Then where /dev/sdX is your root and boot partition # mount /dev/sdX /target # mount --bind /proc /target/proc # mount --bind /sys /target/sys # chroot /target # /usr/sbin/grub-install /dev/sdX # /usr/sbin/update-grub /dev/sdX # exit # umount /target/proc # umount /target/sys # umount /target # reboot That's how I got around a failed grub install due to a screen corruption bug with the Belenos betas text mode installer. But that was much later in the process, so it might not work for you.
