The closest I got was using
mkisofs -J -r -l -b 0000Boot/0000Kernel.BIN.C -no-emul-boot -o Temple.iso TempleOSCD/
The kernel gets loaded, but fails to identify the boot drive, asks for the I/O port number and then crashes.
Perhaps not all of the kernel gets loaded. (tested on QEMU)
What the built-in ISO9660ISO function does to produce a bootable image, is use a small Stage-1 loader and binary-patch in the kernel's raw on-disc location. Which is, needless to say, pretty clunky.