Connection Pooling directly on Postgres Server

I'm looking for connection pooling solutions for our php/apache server.

I already checked pgpool and pgbouncer but during the tests, I had the
following (mad) idea...

Why not to implement a connection pooling server side as apache for
example does?

I try to explain my idea...

The postgres server maintains a number of connections always alive (as
apache for example does)
even if a client disconnects.

The following parameters could be used to tune the number of connections
kept alive server side:

StartServers: number of postgres already active connections at server start
MinSpareServers: If there are fewer than MinSpareServers, it creates a
new spare (connection)
MaxSpareServers: If there are more than MaxSpareServers, some of the
spares (connections) die off.

The parameters has been taken directly from an apache httpd.conf sample...

Could it be possible to implement a similar solution on postgres?

What to do you think about this?

Thank you,
Denis