A possible route could be to find someone with a PowerBook G4 12", link it to the Pismo with a Firewire cable then start the Pismo in Firewire disc mode. Run the OS X installer on the G4 and select the Pismo's drive as the destination. As far as the installer program is concerned it is installing OS X onto a drive on the PowerBook G4.

This workaround of model-specific install discs does work, I've tried!