You shouldn't need to configure Apache to be 'ELB / CF aware'
Have you added Alternate Domain Names (CNAMEs) entries to your Cloudfront Distribution configuration?
** Update **
Try forwarding your host header to the origin. You can do this by editing the behaviour(s), setting 'Forward Headers' to 'Whitelist' and adding 'Host' as a custom header, then allowing the changes to propagate.