CREATE TABLESPACE dynamically

I am writing scripts to create a database that I want to run in my
development, testing, and production environments. That means I need to
be able to do something like

IF <condition>
CREATE TABLESPACE foo LOCATION E'C:\database';
ELSE
CREATE TABLESPACE foo LOCATION E'Z:\database';

I can't seem to find a way to do this, for two reasons:
1) I can't do IF statements unless I create a PL/PGSQL function. And a
PL/PGSQL function cannot issue a CREATE TABLESPACE command.
2) The CREATE TABLESPACE command does not allow expressions.
CREATE TABLESPACE foo LOCATION 'FOO' | 'BAR'
is not valid. I'm not sure I understand why since that is an expression
that yields a string. Parenthesis don't help either.

Is there any way I can do this?