You'll need to mount them at a different location, first, copy data over, then overmount the real location. eg:
Code:
## assuming /dev/xvdc is your new /usr
mount /dev/xvdc /mnt
cp -a /usr/* /mnt/
umount /mnt
mount /usr
Note that in the case of /var and /tmp, rebooting afterward is recommended. Also, once you're sure things are working fine, you can remove the unneeded copies in the root fs like so:
Code:
mount --bind / /mnt
rm /mnt/usr/* -rf ## don't remove /usr itself!
umount /mnt
Be sure to copy everything, and make sure it comes back on a reboot, first, of course
