switching db's on the fly

after connecting to a db under pg 7.2.x using the url, is it possible to
switch to another db hosted on the same machine without reconnecting?

i have a setup with several databases all hosted on the same server with
the same db owner etc. i've written my own pooling but then i need to pool
for each db which, given the number of db's, means i end up with a lot of
idle connections using resources.

what would be better is to be able to switch to the appropriate db
when the connection is retrieved from the pool. this then pools
connections between db's as well. i understand there's some mgmt involved
with access to the db on a switch, but i believe this is easily managed.

under mssql server you can use the USE <database> command.
Is there some equivalent or some hack possible?

toby