[Zope] Problem with ZPsyopg

[David]

Zope 2.7 / ZPsyopgDA / PostgreSQL7.3.4

My problem is that we're running a lot of little websites on a single 
server. Each site has its own zope/zpsyopg instance and its own 
postgresql database. But all databases are served by a single 
postmaster (postgresql instance).

The issue arising is that I'm reaching max_connections (and as this 
ties into memory, there are limits to how high I can set this without 
affecting the performance of the machine), while most connections sit 
around being idle most of the time.

I had a look at pgpool, but if I understand it correctly, it won't help 
(or will any other pooling solution), as it requires as many 
connections to the backend, as it's serving to clients. (Or did I get 
this wrong?) I do understand how I can reduce the number of threads 
within Zope to reduce the number of connections, but that only goes so 
far.

Is there a way how I can configure my system, so that idle connections 
expire when not used for a certain time? Or is there another solution 
to the problem?

Thanks

DR