Hi Frank43,
I am afraid the autoboot behaviour is not controlled by CHDK but by the camera's original firmware. I think some of the developers explained that the trick with locking the card is probably reserved for service use by Canon in their repair offices. CHDK in fact uses the locked card only as trigger for the automatic boot. Once the camera starts up, CHDK just tricks the camera that the card is not locked and therefore photos can be written without any problems on it.
So locking the card is definitely a requirement to autoboot CHDK.
Regards,
Zdravko