I suppose you could use GRUB and whatever Coreboot has as its BIOS? Either way, sad times indeed when PCs aren't anymore.
EDIT: The answer is yes and it's been done: https://g00se.org/2016/11/seabios-on-libreboot.html (granted, that's booting directly from coreboot to GRUB, but it should be the same booting UEFI to GRUB AFAIK)