Hi,
I did not try to mount during the boot the extra slices on my SD-card, but is it not easier just insert the mount string at the end of the "start" section in the file "/etc/init.d/sd" ? And, sure, umount in "stop" section.
Sorry, if it is so stupid, I am a novice in Zaurus. But it looks more natural. Of course better is to edit the "/etc/fstab", but it is more dangerous, IMHO.