Code igniter custom Database class

I need a Coder familiar with Code Igniter custom classes. What I require is a custom database class written (or code Igniter's database class modified) to accept 2 databases at the same time. I know it can accept 1 database from the 2 groups as active, but that way it queries any 1 database only. What I require is the ability to pass query like, "SELECT [login to view URL], [login to view URL] FROM [login to view URL], [login to view URL]" And also all the JOIN functions etc should work as normal with Code Igniter.