Passing Parameters to copy_expert()?

Hi,

I'm trying to use the copy_expert() command to dump records from a database
to CSV.

http://initd.org/psycopg/docs/cursor.html#cursor.copy_expert

However, I need to pass some parameters into the SQL statement - namely the
values for a WHERE IN clause.

(Basically, the COPY operation is too big for our PostgreSQL server to
handle, so we're chunking it up into multiple queries - hence, needing to
pass in values to WHERE IN).

I can't seem to see anything in the docs about this about how to pass
parameters through to copy.

I could use Python's own string interpolation, however, I'm under the
impression that's a pretty bad thing.

Is there another way to pass parameters to copy_expert()?

Cheers,
Victor