Libreboot dose not use seaBIOS but can be used with seaBIOS
i found this tutorial but its apparently outdated https://github.com/bibanon/Coreboot-ThinkPads/wiki/Compiling-Libreboot-with-SeaBIOSbut i know for a fact as Libreboot is based on Coreboot you would be able to use seaBIOS with it so you could try asking
on the #libreboot IRC channel also libreboot's grub payload can boot from usb
