Installing multiple instances of Postgred on one FreeBSD server

I need to migrate a production database from Postgres 9.0 to Postgres 9.2.

Running FreeBSD 8.1/amd64, and presently running Postgres 9.0.4.

Due to the nature of the application, I cannot have any considerable downtime, so the pg_dump and install new version route is not an option.

I would like to install PG 9.2 on the same server and use Slony to replicate the databases, and once everything is up take the 9.0 cluster down.

Ideally, I would like to do this from the ports.

Any suggestions will be deeply appreciated.