Nishanth - as a Cobbler newbie, I didn't know about this. Thanks!
It worked after I tweaked it - I had to add the kernel parameter "root=live:/boot.iso" to the PXE config line, where "boot.iso" is the name of the original ISO that livemedia-creator made before getting PXE converted.
For others finding this on the internets, I had to make a profile called "livecd" with the distro, and then I had to add the kernel option to the profile with the following command:
cobbler profile edit --name livecd --kopts="root=live:/boot.iso"
It works! :D Thanks all!