Option: theme_advanced_custom_layout

This option is used to specify a custom layout manager function. The format of this function is: customLayout(template) where template is the template array within the advanced theme, this function should return a new template array containing the editor HTML in a key called html. This option can only be used when theme is set to advanced and when the theme_advanced_layout_manager option is set to the value of "RowLayout". CustomLayout template

Example of usage of the theme_advanced_custom_layout option:

function myCustomLayout(template) {
    // Make custom layout
    template['html'] = "make new layout";

    return template;
}

tinyMCE.init({
    ...
    theme_advanced_custom_layout : "myCustomLayout"
});