It is best to hire someone to do such customizations. Here is the change required –
1) Pls modify the line number 133 of framework/presentation/custom-post-types.php file to –
'supports' => array('title', 'editor', 'thumbnail', 'page-attributes', 'custom-fields')
2) Enter a custom field named mo_custom_url to the class in the class edit window. Pls search Google for more information on Custom Fields in WordPress if you have not used them before.
3) Insert the following code into framework/functions/post-functions.php file at line number 667 –
$custom_url = get_post_meta(get_the_ID(), 'mo_custom_url', true);
if (!empty($custom_url))
$post_link = $custom_url;
That should do it. Pls give a try.