Hi!  Please include in next release of openssh the following trivial
patch to sshconnect.c.  It is useful if some program connects
to the server and exec ssh with open two fd.  In this case there
is no need of ProxyCommand.  I use this with DJB (http://cr.yp.to)
tcpclient.  I have in ~/.ssh/config

Host myhost
HostName 1.2.3.4
...
ProxyCommand -UCSPI 6 7

and I start ssh like:  tcpclinet 1.2.3.4 22 /usr/bin/ssh myhost

With the current ssh configuration in most cases ProxyCommand do only
read/write.  May be other programs use different numbers for
stdin and stdout sockets fd.  Tcpclient user 6 and 7.  One
have can to put the numbers after -UCSPI option.  May be some
line in ssh.1 is also a good idea.

        int pin[2], pout[2];
        pid_t pid;
        char *shell, strport[NI_MAXSERV];

+       if (sscanf(proxy_command, "-UCSPI %d %d", pin, pout) == 2) {
+               packet_set_connection(pout[0], pin[0]);
+               return 0;
+       }

        if ((shell = getenv("SHELL")) == NULL)
                shell = _PATH_BSHELL;

        /* Convert the port number into a string. */