How to select the source ip address for a connection to the database server

Hi,

I am currently working with PHP5+PGSQL 8.2.13 and i have the
following problem to solve and i need your help.

The server hosting PHP+psql client has 1 physical network
interfaces with multiple subinterfaces using different IPs.

One of those IP is dedicated to my domain, but it is not servers
default IP address since i share the server.

So the problem that i need to solve is how am i going to be able to
use-select my domains IP address as source to connect to the remote
databases.

Is there any configuration to settle default source IP the client will use?

At the moment all my attempts to connect to the database make use
of servers default interface IP as source.

Thanks in advance for your help.