I changed the ownership of /hdd1, /hdd2 and /hdd3 to zaurus, group qpe, so that the files could inherit the ownership and thus the directories would be automatically writable by user zaurus
To do so, I had to remount / as rewritable ("mount -o remount,rw /"), "chown zaurus:qpe /hdd*", "mount -o remount,ro,noatime,ro /") or some such similar thing.