Don't know about squid. But stunnel -T certainly can do it, but it naturally needs kernel patch to be allowed to specify the peer IP when RDRing the packet. I don't think IPFilter lets stunnel do this as is.
I think it does. I'd have to check the API to be sure though - it's been a while since I abandoned my user-space FTP proxy. And it may require privs for the IOCTL.
-- Carson
