Messing around with cbagger's mkwriteable script, and came up with something that allows the user to specify which directories to open up. I figure this could be useful for someone who is sensitive to RAM usage but also wants to be able to write to a particular directory or directories.
This hasn't been thoroughly tested, but it seems to work.
grep ^all $checkfile && exit
cp -srd /KNOPPIX/bin/ /ramdisk
ln -sf /ramdisk/bin /
echo "bin" >> $checkfile
cp -srd /KNOPPIX/boot/ /ramdisk