Ok Bill -- you forced me to get off my lazy butt. 😉 After unpacking my powerbook and after rummaging through a stack of CDs for a blank one, I did a test (my stack of "burned but never labeled" discs is beginning to shrink since I finally got a thumbdrive -- at least I tossed half a dozen useless discs).
First thing, the command that replaces "scanbus" is "dev=help". It may or may not be worth a try -- it returns false info for me, telling me I should use "dev=IOCompactDiscServices" when in fact, it won't work unless I use "dev=IODVDServices" (I have the cd burner/dvd reader -- not the superdrive). After sorting that out, I used the following on a "damX small linux" ISO (I can't actually name this linux distro here -- replace X with "n"), took it over to my desktop and it is now happily booted into DSL.
cdrecord dev=IODVDServices speed=16 -data -eject dsl-1.5-syslinux.iso
Of course, one must be rootish to do this, either through sudo or as actual root. I'd throw in a "-v" for a progress bar. I set the speed to 16 because I wasn't sure what my combo drive will do and figured it would take more time to find out than to burn -- so I just picked a conservative number (probably not even needed anyway).
Hmmm, maybe I should find a sharpie and label that DSL disc. 😉