The kernel command line, including your "custom" boot codes, is available after boot in /proc/cmdline, so you can parse that to pick up the PRE and RUN values.
/opt/bootsync.sh runs as root as one of the last steps in the boot sequence, so that would be a likely place to do your scripting.
If your scripting requires bash then load bash.tcz "onboot". If you are using vanilla scripting that can run under the busybox ash then you don't even need that.
If the value you show in PRE is a complete command, it looks like you will be mounting /dev/sdb1 on /mnt instead of on /mnt/sdb1. Since Core, by default, mounts file systems in /mnt/<device>, mounting one on /mnt would likely make things interesting if anything else were previously mounted. If your tce directory happens to reside on /dev/sdb1 then it ( /dev/sdb1 ) will be be automatically mounted on /mnt/sdb1 during boot.
Edit: Clarification of "it" in last sentence. 2013-06-27 11:28 edt