Change date format through an environmental variable?

I want to get Pg (v7.4.7) to output a date field in a different format 
than yyyy-mm-dd through the use of an environmental variable (because I 
have no access the SQL).  Is this possible?  I know about the DATESTYLE 
variable, but that seems to work only within a query transaction, and 
has no effect if trying to set it as an envvar.

Mark