Sure: Do the following:

1. qemu-img create test.img 10G
2. qemu-system-x86_64 -enable-kvm -hda test.img -cdrom ubuntu.iso -boot d -m 512
   
3. Install ubuntu on test.img

After installing, boot the new virtual machine with your self-build bios:

• qemu-system-x86_64 -enable-kvm -hda test.img -m 512 -bios build/coreboot.rom
  

See how the machine starts successfully, using the 'broken' seabios. Ubuntu boots successfully. Even starting my Windows7-machine nearly works, but while "Windows is loading files" is written the virtual screen / text becomes yellow and booting stops.

But Ubuntu can successfully be booted and used absolutely normaly with cb+seabios - only installing seems impossible and the errors you (Jonatahan) described, appear.

Greetings

If I build a new virtual harddrive, install Ubuntu there (using qemu's
default bios) then I'm able to start the new image using my self-build bios.

I'm not sure what you mean here. Can you explain it in more detail?