Here is my config file for a kernel version of linuxbios. opteron_phase1_p4_noapic is a kernel that I ran mkelfImage on.
Let me know if this works, I just quick hacked it for the new config scheme but it is untested as of today.
target hdama mainboard arima/hdama option ROM_SIZE=0x100000 romimage "fallback" option USE_FALLBACK_IMAGE=1 option ROM_IMAGE_SIZE=0x10000 option LINUXBIOS_EXTRA_VERSION=".0Fallback" payload ../../../../opteron_phase1_p4_noapic end
buildrom ./luxbios.rom ROM_SIZE "fallback"