Would Trisquel's installer automatically add that boot option to the
installed kernel? If not, I guess one must 'chroot' into the newly installed
system (from the Live system), define GRUB_CMDLINE_LINUX="forcepae" in
/etc/default/grub and execute 'sudo update-grub'. But I hope the installer
automatically adds the options that are used to boot the Live system.
Interestingly, jxself's APT repository for Linux libre has "nonpae" kernels:
https://jxself.org/linux-libre/
I believe he must know how to install Trisquel on computers that do not
support PAE.