IIRC they load something to the Mac ROM memory space on startup that reads the PRAM for a flag to enable or disable the PPC, and the PPC does not work if that flag is not detected. That flag is set using the Mac OS control panel.
Then shove the control panel in the Extensions folder and rename it to load before the Linux/BSD boot loader. If that doesn't work, identify the PRAM value that is being set and use one of the many PRAM loaders to set it during startup. It is always worth a try.
Has this control panel/extension switcharoo worked with something else? How do you rename something to make it load first?
As far as I know, the two ways to run BootX: as an application or as an extension, "and the only difference between the application and extension is that the extension has a (ResEdit-configurable) timeout value, after which the default OS (which the user defines) is chosen. If Linux is selected, BootX shuts down the Mac OS, loads the Linux kernel into memory, and starts it running. If the Mac OS is selected, BootX simply exits."
I think the minute the Mac OS shuts down, everything gets reset, and the system gets confused about which CPU to use again- I have vague memories of such a problem with trying to run linux on a DOS Card Mac. A big problem is that the Mac Boot Rom is completely closed and proprietary (unlike the reverse engineered PC BIOS, while not "open source"-- its workings are well known) It is the Boot ROM settings, not PRAM settings, which causes problems.