To be honest I'm not exactly sure when it was added. The link refers to 9-CURRENT so it's rather old. Try following the procedure using 10.3-RELEASE or 10-STABLE. Both FreeBSD 8 and 9 have been End-of-Life for quite some time.
I seem to recall the option of being able to redirect certain output to stderr using something like somecommand 2> error.log but can't get it working. Does this not work, or does it depend on the shell being used?