Force one telnet per ssh tunnle

I let users telnet to my aplication using ssh tunnle. The users use
OpenSSH client 3.x as this,

ssh -2 -N -f -L porta:localhost:23 192.168.xxx.xxx
telnet localhost porrta

The server is also an implementation of OpenSSH. My requirement is to
force only one telnet over the tunnle that has been created. For
example the following currently works,

ssh -2 -N -f -L porta:localhost:23 192.168.xxx.xxx
telnet localhost porrta
---- from another shell
telnet localhost porrta
---- from another shell
telnet localhost porrta

But I want that consequitive telnet should fail. Is there a server
setting to acheive this. Any client setting/option to add while
creating tunnle will also work for me, as I can force my users to use
it.

If nothing else then I am also willing to change the SSH server side
code to suit my needs, but I hope that is the last resort.

Thanks.
.