On the FreeNAS installation ISO image, /rescue

is the directory which contains all the executables which run
from the shell.  /usr/bin , /usr/sbin, /sbin , /bin are all symlinks
to /rescue.  To add a new executable to the ISO image, you
need to add it to /rescue.

Add /rescue/less to the ISO, and add /rescue/more as a link to /rescue/less.