Hi,
installing a distro can be done using this guide:
https://libreboot.org/docs/gnulinux/grub_boot_installer.html
modifying the boot menu can be done using this guide:
https://libreboot.org/docs/gnulinux/grub_cbfs.html
I saw "ubuntu" mentioned. obviously you should use trisquel, since it's a
libre distro. ubuntu is non-free. but in answer to your question, see the
above links.
~Leah
PS: prepare the USB stick using dd. not all distros work using the USB option
in the boot menu. If you come across such a distro, see:
https://libreboot.org/docs/gnulinux/grub_boot_installer.html#booting-isolinux-images-manual-method
