Custom Joomla Component Editing (Easydiscuss)

I'm am looking to make a small modification to a plugin. Currently when the plugin creates a post it assigns it to one category. I have changed the category selector to be a multi-select, now what i want to do is when the form is submitted multiple a copy of the post should be created for each category. It is important to note that i want a post to be created for each category and not one post to be assigned to multiple categories. I have attached the two relevant files. The one is the form and the over is the controller which handles the adding of the post. Please reference function submit().