Modifying Wp_Query To Include Other Tables/Fields

Hey,

I am searching the Codex but I do not see such as solution. I have also not find the proper method via google. I am simply looking to find a way to add a table (from a 3rd party plug-in) to the WP Query so it can search posts AND products (products table of my plug-in which is for e-commerce)

I couldn’t find a way to hack the SEARCH TABLES in this codex thread:

http://codex.wordpress.org/Function_Reference/WP_Query#Parameters

Do I just modify the query.php file or would I just build my own query and results and call that if there are ‘no results’ (Since products are never displayed with the default wordpress search bar)

Thoughts? Please note I have spent many hours trying to find it and I promise I have searched before I posted. Ty.