How to set timezone for Postgres psql?

How do I set timezone for psql to something other than my default (US/Central)? Here's what I've tried so far:

$ psql
psql (9.1.4, server 9.0.4)
...

$ psql -c 'show timezone'
  TimeZone  
------------
 US/Central

$ psql --set=timezone=US/Eastern -c 'show timezone'
  TimeZone  
------------
 US/Central

$ psql --variable=timezone=US/Eastern -c 'show timezone'
  TimeZone  
------------
 US/Central

Edit: I don't want to change the server timezone, just the client.

Edit #2: I want it in non-interactive mode.