Segher pointed out on IRC that these days it {sh,c}ould be possible for EtherBoot and coreboot to load a vmlinux ELF directly.
There was some discussion about initrd/initramfs and Martin-Eric expressed the need to combine kernel+initramfs after the kernel was built.
I first thought that would be pretty difficult, but as it turns out it may not be so bad.
I've created http://www.coreboot.org/Initramfs which shows the two steps that are neccessary, in theory. Please test and verify if this works with the popular ELF loaders we know and send us a note.
Thanks!
//Peter