The cdhdtape image is already a bootable image if written directly to the
   CD, it just isn't an iso9660. The El Torito (x86-only, PeeCee-only) boot
   stuff is, AFAIK, completely ignored by alpha...after all, you wouldn't even
   want it to work, as it would prevent you from making a dual-boot CD.  Or
   am I completely on drugs?

well. el torito *could* become an option for alpha but it isn't currently.
el torito is not x86 only....