PQntuples for older version (2.2.1) of psycopg2 with ctypes

I am using cursor.copy_expert and I would like to be able to use
cursor.rowcount but most of the systems I am targeting have older psycopg2
versions on them.

According to the following URL rowcount was updated for use with
copy_expert in 2.5.3...
https://psycopg.lighthouseapp.com/projects/62710/tickets/180-return-number-of-rows-for-copy-operations

Inspired by:
https://github.com/sunlightlabs/psycopg2-ctypes/blob/master/psycopg2ct/_impl/cursor.py

I wonder if it is possible to use ctypes to do this... Something like this
maybe:

import psycopg2
import ctypes
libpq = ctypes.CDLL('libpq.so.5')

conn = psycopg2.connect(foo)
cursor = conn.cursor()
cursor.copy_expert(bar)

rowcount = libpq.PQntuples(???)

I can "read" the psycopg2 source but I am not fluent. I am having trouble
working out what 'pgres' is. Is it the fileno() the backend_process_id()
etc...

So far all I have manged to do is segfault my python processes. Woot!

Is 'pgres' exposed by the Cursor or Connection classes somewhere?

Regards,
-Alan