Please look at the attached source taken from a patched version of the 7.4
driver, which is a little out of date with respect to the latest drivers.
However it gives you the idea of what you need to do in order to modify one
of the latest drivers.
The main problem with all HTTP style proxies is that you can only specify
ports 80, 443 and sometimes 8080 and or 8000.
I've spent a lot of time with proxies and to get a reliable connection you
need to use SSL on port 443.
This means you must redirect incomming requests, on the firewall that serves
requests to your PostgreSQL server, from port 443 to port 5432. Which also
means that you cannot have a secure web-server on the same IP address as
your PostgreSQL server!
Regards
Donald Fraser