connect with a tunnel JSSE ?

hello,

i have a tunnel betwen a Java Client software 'JCS'
and a Java Frontal Server 'JFS'. (working fine).
they are talking SSL + special auth system.
the JFS is forwarding connexion in the tunnel
to a postgres server 'PS' behind him.
the JCS can't see the PS directly.

tunnel direct
JCS /==========/ JFS /----------/ PS

PROBLEM : the JDBC driver is designed to connect
by himself from JCS to PS. it won't work here.

QUESTION : Do you know how i could ask the jdbc
driver to send the connection in the tunnel from
the JCS and not trying to connect directly ???
do you know a way to choose my streams in driver ?

POSSIBLE SOLUTION I DON't WANT : i could listen
from the jcs and configure the driver to connect
to localhost, like i would do with a
ssh port forwarding.
i won't because i want to allow connections only
from this JCS, not localhost.

many thanks for your help.