From LedHed's Wiki
If you need to install a standard FreeBSD package or "Port" on a pfSense based firewall do the following:
fetch -o - "ftp://ftp1.us.freebsd.org/pub/FreeBSD/ports/ports/ports.tar.gz" | tar zxf - -C /usr
Reference
pfSense Forum: http://forum.pfsense.org/index.php/topic,2904.msg18021.html
FreeBSD Ports HowTo: http://www.freebsd.org/doc/en/books/handbook/ports.html