That thread has some incorrect information, partly because the original poster tried added the filter function to the theme’s functions.php file, then resorted to hacking the WP User Integration plugin.
Here’s the correct solution:
1) Set up a site specific functions plugin.
2) Add this line of code to the plugin: add_filter( 'EED_WP_Users_SPCO__verify_user_access__perform_email_user_match_check', '__return_false' );
3) Activate the plugin.