Scouring groups.google.com revealed this page:
http://lists.linuxppc.org/linuxppc-user/200005/msg01454.html
Which is an excellent resource.  However it is for Linux.  It basicly 
says to send the hex string 0x011301 to the CUDA chip.  In linux-powerpc 
  the CUDA chip is accessible via /dev/adb.  So with a file containing 
those three characters, you can essentialy do a "cat 3bytefile > 
/dev/adb" and the system will turn itself on in the event of power 
applied to it after a power-outage.

I've tried this verbatim in netbsd-macppc-1.6.  It doesn't work: it 
results in: "cat: stdout: Operation not supported by device".  How would 
one make this work?

Any help on this is grately appreciated!