How to modify *.wsgi file to specify settings.py file for multiple sites running on one instance of OSQA?

Saw with great interest Evgeny's answer to this question here about setting up more than one site to run on a single OSQA install.

Here were the steps outlined as to what was needed for each site:

1. an empty database
2. settings files, e.g. site_a_settings.py and - site_a_settings_local.py
3. *.wsgi file (and within specify which settings.py to use)
4. directory for uploaded files (server-writable) - and save path to that in MEDIA_ROOT settings parameter (in your site_a_settings_local.py)
5. run python manage.py --settings=site_a_settings.py syncdb to create the database (always use --settings option with the manage.py with multi-site setup)

I think I understand all steps except step 3. I looked at the existing .wsgi files, and poked around parts of the Python documentation, but couldn't see how to accomplish step 3.

How would I specify the particular settings.py file in the *.wsgi file?

Thanks!