How do I fallback to boot from local hard drive in iPXE script?

view story

http://serverfault.com – I have a script being loaded from iPXE. What I want is to make the script fall back to boot from a local hard drive (or CDROM) on failure to boot from the san. The idea is allow installation of an Operating System onto the SAN target from local CDROM or USB drive. I can't see anywhere that in the iPXE documentation that tells me how to boot from a local internal drive. How do I do this? (HowTos)