Hi.
First, I am very new in everything related to OE and Zaurus (worse, this is my first post as well!!!) , but I think I can help you. I don't have my zaurus here, so I cannot check anything now.
If the Zaurus/OE manages this in a more or less standard way in Linux, you should have a look to the file /etc/fstab. I bet there is a line there that mounts your SD, look for the keyword sync. If your are going to modify it, MAKE A COPY OF THE FILE JUST IN CASE and store it in the internal memory.
You can find further help here:
http://www.tuxfiles.org/linuxhelp/fstab.htmlGood luck!
E