Multiple domains, one WordPress (not multisite)

I need to map/a-record/cname multiple domains to a single WordPress instance.

example:
domain1.com/about/
would be the same as
domain2.com/about/

I can do this just fine but I also need to make sure any links that are generated through WordPress point to the current domain they are one.

For instance, the "Next Post" link, navigation links, guids, EVERYTHING, stays on the current domain.

Note:
I don't want multisite as the domains need the EXACT same configuration, just different domains.

I'm going to fool around with:
define('WP_HOME','http://example.com');
define('WP_SITEURL','http://example.com');

Any other ideas?