Tips for searching categories and/or tags with Global Site Search?

The Global Site Search plugin has gotten me almost where I need to be with a multisite search, but I really need the ability to include tags and/or categories in the query. It doesn't look like Global Site Search supports that, but it does look like Post Indexer captures that information. Could anyone point me in a direction that would help me alter the query to include these pieces? Just looking for a little guidance, thanks!