Is it possible to mount a partition on the hard drive that somehow is also scanned along with rc.local (or wherever the appropriate startup files go)? I want to boot a live image and have something automatically run but I can't change any files in the Live Image. Is that at all possible?
It is possible if and only if the live CD explicitly supports it. You could have
I suspect the easiest approach would be to boot from USB instead of CD, and run a script on the USB drive.