I'm trying to figure out how to build coreboot such that I can boot both legacy and UEFI systems.

From what I can tell, most payloads will load either one or the other, but not both (unless Grub2 can do this - unclear to me).

On the other hand, is it possible to use tianocore + SeaBIOS as the primary and secondary payloads, respectively? Or vice versa, I guess. If so, how would one go about setting that up? 

Menuconfig doesn't let me set arbitrary secondary payloads, so I'm guessing I'd have to stuff it in the CBFS manually somehow, yes?

Cheers,

Rafael