I've fleshed out a basic busybox style thing based on the crunched binary stuff which generates sysinstall and the rescue binaries. Thankfully, most of the hard work (read: the hacks needed) are done for you - both in the rescue Makefile and the general FreeBSD build framework.
So, I give you "bsdbox" - a not-so-small static binary busybox style solution to help build a standalone image.
# ls -l /sbin/bsdbox
-rwxr-xr-x 1 0 0 2958668 Sep 16 17:44 /sbin/bsdbox
ls cat dd df cp hostname kill mkdir sleep sh -sh dmesg sysctl init reboot
mount mdmfs mount_mfs mdconfig newfs ifconfig route ping true false hexdump
tail netstat chown chgrp arp hostapd hostapd_cli bsdbox
And with that, I have this TP-Link device happily running FreeBSD as a WPA-enabled wireless access point.
Combined with the GEOM uzip module, the entire filesystem (which is the above binary and a few shell scripts) - is just slightly above 1 megabyte in size. (geom_lzma will make that even smaller.)
The bsdbox stuff is in my GIT repository in "bsdbox". It's built as part of the base system and installed in /bsdbox/. The binary can then be cherry picked and built into an image with whatever symlinks are needed. There's more to do - more binaries for a start; but also making it a bit easier to configure bits than a single Makefile - but it's useful right now.