We have solved this by adding CSS classes named something like "float-left" and "float-right." We then place these in the "Custom CSS Class" of the modules that we want floated. It works quite well and there is no need to make changes in mojoPortal for it to work. Take a look the CodeBox site for an example of this. The "Latest News" and "What Our Clients Say" sections are both in the Center pane.