[Answered ]-Use Django flatpages without sites

You need to configure your webserver correctly so that the requests from all domains get forwarded to your only django instance! You cannot run flatpages without having django.contrib.sites in your INSTALLED_APPS, but that is no problem for your case, the actual site will always be determined with the SITE_ID defined in your settings.py. The sites framework does not check the request to check which is the actual site. If you run multiple sites, you have to run multiple django instances that use different settings, which define different SITE_IDs!
So just check your webserver to have everything directed to your django instance!