tproxy on freebsd

[zen]

hi,
i know it seem out of topic,
i recently build a proxy server to serve our small ISP,
but i'm facing a big problem. as far as i know FreeBSD didn't support 
TPROXY like linux had.
but i need to build this proxy transparently so only my client ips that 
visible when browsing.
i use ipnat and ipf with Squid latest stable release.
does anyone has experience building a true transparent proxy with FreeBSD?
please share the knowledge and the regarding this problems.

TIA

Zen