Also, given the problem I had, rsh probably would not have worked since sh and ssh were not working either.
Remember, /sbin/sh needed to be staticly linked, not dynamicly linked. So you can't use /usr/bin/sh. A dynamically linked /sbin/sh will probably render the box unbootable.
I don't think that the box wont boot. Just that in case the /usr filesystem gets corrupted, root won't be able to login to fix it.
blowtorch, the attempt to mount /usr occurs in /sbin/rcS and the first line of that is:
#! /sbin/sh